I was wondering what would happen if the main branch of the Romanovs died out in 1899. I don't know of any specific event that might work as a POD, but I simply want it to happen before Nicholas had the opportunity to completely ruin things.
I think this would leave the throne of Vladimir Romanov, Alexander II's next son in line, and leave him with about 10 years on the throne to try and salvage things in. From what I understand Vladimir was rather more cultured, better educated, and less of a religious fanatic than Nicholas. He had held various high posts in government and in the military. He was also at odds with the more conservative branches of the Romanovs. This is before Bloody Sunday in 1905 where his reputation was tarnished, so he should be in pretty good standing with the general populace.
I have probably missed a ton of details, but what and how do people think a Vladimir IV Romanov (would it be IV or I?) would do things differently?
Definitely Vladimir I Alexandrovich. Grand Duke Vladimir Kirillovich claimed the pretendership under that regnal name, so chances are his grandfather would have reigned as Vlad I. Really anything that avoids Alix the Neuritic and Rasputin can only be a plus for Russia.
The way I understand it, many members of the Romanov dynasty - such as Michael, Grand Duke Nicholas Nikolaevich, and even Nicholas II - came across as moderate when compared to Vladimir.
It's true that Vladimir was not particularly responsible for Bloody Sunday; but there are plenty of other venues where his politics and personality shone through. He did insist that those who were responsible for the Sunday chaos go unpunished and be allowed to keep their positions. He was outraged at the very idea of having a Constitution, even a very weak one. He staunchly opposed Nicholas II's gift of crown lands for the Stolypin land reform. He was a kneejerk Anglophobe and apparently a supporter of the Hamidian regime (if only because of that kneejerk Anglophobia). And so on.
It seems like 90% of Nicholas II's bad decisions were made on Vladimir's advice, under Vladimir's pressure, or at the very least with Vladimir's approval. While 90% of his good decisions were made against Vladimir's opposition. I could be wrong, but everything I've read about Vladimir basically paints him as a pompous ass, all ambition and no quality (such as Robert Massie's biography of Nicholas; and Montefiore's book isn't exactly overflowing with praise for him, either).
Nicholas, for all his many faults, was at least humble, occasionally open to compromise and reform, and had a strong sense of duty.
So he was a Romanov then? Good to know

!! But in all seriousness you basically described most of the senior Grand Dukes at the time. They were all basic Anglophiles, thought constitution was the worst type of curse word, thought that the peasents should know their place, ex ex. Vlad wasn't the best by any means but blaming him for Nicky's failures is shifting the blame. Nicky and Alix made were able to make their horrible decisions all on their own. The best you could blame him for would be events before bloody Sunday and his son Kirill eloping with Alix's former sister-in-law, Victoria Melita of Edinburg-Saxe-Coburg; after those evens Vlad was in disgrace with the Tsar.
The problem with George becoming Tsar is that his weak health made it incredibly difficult for him to live outside the Caucasus, with him staying in Likani after he was diagnosed. A Tsar who can't live in the capital creates all sorts of difficulties, and with his weakened health it is only a question of time before he dies.
One could easily have the POD be that he never develops Tuberculosis in 1890. Before then there didn't seem to be any major concerns with his health.
Since it was only a year later OTL that Count Witte et al got into a fight about what should be done were Nikolai to die of typhoid leaving Alicky preggers with what they hoped was a tsarevich (spoiler: It wasn't). Would there be any branches that might support a female succession (particularly if they've got age-appropriate son(s) to marry the Big Pair)? Or that just don't like the Vladimirovichi so they support the press for Empress Olga Nikolaïevna. But even if thats the case, what happens with Alicky? The last Russian empress dowager not the next emperor's mom was Elizabeth Alexeïevna (if we remove Ekaterina Dolgurokova from the list). She'd probably prefer the privacy etc, but at the same time, Ican still see her having the desire to meddle (which Mieche-Miechen might not stand for).
In the end, I guess it depends mainly on Nicky and Misha's mode of death. If Nicky's ill and knows he's dying he might allow Misha to marry Baby Bee as Misha wanted OTL, or attempt to fiddle with the succession to allow Olga to succeed. Whereas if they're assassinated or a motorbike accident (like brother George and Misha's son), then I can see the court being thrown into a sort of chaos depending on whether Alicky's given birth to Marie or not (ergo the hoping for a tsarevich or the disappointment of knowing it's impossible).
This is a very difficult question. No branch would support altering the succession, especially sense it would mean a regency in this instance. Now, legally speaking the Tsar is the absolute Sovereign and needed no consultation or registration of his decrees to make it official, binding or legal. So from a legal POV if Nicky lay dying he could summon the Ministers, proclaim a change to the Pauline laws and make little Olga the Tsesarevna. However, in practice highly unlikely to go through. First there's the question of whether the Tsar can change laws on the death bed, then his mental state would be questioned. Then the Church, government and army would be involved. Most likely the Court and the family will find/invent a reason to suppress/ignore such a decree and the next Grand Duke becomes Tsar.
Now if Nicky dies and Alix is pregnant, well there's precedent for that as well. In the case of the deaths of Louis X of France and Alfonso XII of Spain, the throne becomes vacant and a regency is set up. If its a boy, then he's born King (or Tsar in this case). If its a girl, the the next in line succeeds.
Nicholas when ill with typhoid did in fact at Alexandra's urging discuss altering the succession to allow his eldest daughter to succeed in the absence of a male heir - it was pointed out that he would struggle to get it through. As most of his family would be opposed to it - whilst amending the family laws was technically possible there was a real reluctance to alter the essential elements of the Pauline Laws. Given there were numerous male Romanov's around he couldn't even say it was necessary.
the chance of marrying Olga to Kyril is remote - Marie Pavlovna (Miechen) loathed Alexandra after her attempts to help the young Empress were rebuffed. Kyril himself had been in love with his future wife for some time despite her being pushed to marry Alexandra's brother Ernie.
In terms of contenders its a long-haul to get anyone better by 1899 - numbers 5,6, 7, 21 are all involved in dubious relationships not sanctioned by Alexander III or Nicholas II. 9 was declared insane. I have only included children born before 1900. Of the below - the Mikhailovichi were more liberal in views than the rest but were the lowest down the succession list.
The motley crew usually means that people tend to opt for Nicholas II's death (after George's death) leaving the throne to Michael - because the rest are such an appalling choice.
1) Vladmir Alexandrovich
2) Kyril Vladimirovich
3) Boris Vladimirovich
4) Andrei Vladimirovich
5) Alexei Alexandrovich
6) Sergei Alexandrovich
7) Paul Alexandrovich
8) Dmitri Pavlovich
9) Nicholas Konstantinovich
10) Konstantin Konstantinovich
11) Ion Konstantinovich
12) Gavril Konstantinovich
13) Konstantin Konstantinovich
14) Oleg Konstantinovich
15) Georgy Konstantinovich
16) Dmitry_Konstantinovich
17) Nikolai Nikolaevich
18) Peter Nikolaevich
19) Roman Petrovich
20) Nicholas Mikhailovich
21) Michael Mikhailovich
22) George Mikhailovich
23) Alexander Mikhailovich
24) Andrei Alexandrovich
25) Feodor Alexandrovich
26) Sergei Mikhailovich
Basically this. Michael was fairly moderate, even liberal. At least in comparison to the rest of the family. However, I do remember reading about a rumor in the early 1910s that would have had Olga marry Grand Duke Dimitri (the only Grand Duke of the next generation until Prince Vladimir Kirillovich was born in 1917) , with the two (or just Dimitri, can't remember the details) appointed as the heir, displacing Alexei. Or at the least the next in line after Alexei. Of course, Olga was against the match and any behind the scenes dealings over the succession fell through. Dmitri's later actions against Rasputin rendered the entire thing null.