While I was typing my reply
@RGB has already given a one I almost fully agree with. I would still post mine as it is a bit more detailed and also so that my effort would not be wasted).
While I cannot definitely answer your questions here are few thoughts (some of them are probably pretty obvious or consist of OTL-history summarization but I would still right them down for rhetorical reasons):
1. In my opinion Muscovite Feudal War was if not outright inevitable had very deep reasons. It addressed two very important issues – the laws of succession and the degree of local princes autonomy.
a) Laws of succession. Before the Civil War succession in the Grand Principality of Moscow was uncertain. There were at least 4 conflicting traditions each sharing its degree of legitimacy. First one is when the khan of Golden Horde appointed the great prince of Vladimir by giving him special document yarlyk (of course by XV century Muscovite vassalage was pretty loose; in practice by that time yarlyk usually was simply an official recognition by the Horde of a new leader in exchange for some minor concessions from Muscovy). Second one was traditional Russian agnatic seniority (lestvitsa) when brothers of deceased monarch had priority over latter’s sons. Third one was the traditional male primogeniture that became increasingly more popular because of foreign influences (and advantages of the system). Forth one was the will of the late monarch.
The whole mess happened because there were conflicting wills (of Vasily I, the father of Vasily the Blind, which favored the latter, and of Dmitry Donskoy, the father of Vasily I and Yuri of Zvenigorod, which stated that after Vasily I Yuri should rule) and the fact that second tradition favored Yuri while the third – Vasily II.
While the civil war in that particular circumstances can easily be butterflied (say Yuri dies before Vasily I) I don’t see clear succession laws being established without the Great Feudal War and thus similar sort of conflict would probably happen in some other generation. I guess the most plausible alternative to this is recognition of the late monarch’s will as the primary mechanism of succession. But again sooner or later a monarch would die without a will or there would be conflicting wills of several monarchs and again some sort of succession crisis is bound to happen.
b)The autonomy of local princes. By XV century the Moscow Rurikids were unchallenged Grand Princes of Vladimir and thus had authority over smaller princes there (e. g. princes Shuysky and Kurbsky that were descendants of pre-Muscovite princes of Suzdal-Nizhny Novgorod and Yaroslavl respectively). Additionally Muscovite princes created appanages for their younger sons (thus creating principalities of Serpukhov, Mozhaisk, Zvenigorod, Galich etc.).
While Grand Princes of Moscow were recognized by all smaller princes as their liege it often was a nominal and pretty loose vassalage. The Civil War however allowed Vasily to annex a substantial portion of smaller principalities (curiously enough not only belonging to his opponents but also to some of his firm supporters like Vladimir the Bold of Serpukhov) and reduce greatly the autonomy of others.
While I guess the power of smaller princes can be curbed without dynastic civil war, it is a very tricky process and would still lead to serious troubles. Not having an excuse of Civil War would make this process look less justified and would take more time.
2. While there are some possibilities of expansion that Moscow probably skipped because of the Great Civil War, smaller Russian principalities like Novgorod, Tver or Ryazan are probably not among them. The last one fell firmly into Muscovite because of dynastic dynamics (in 1456 Vasily Ivanovich inherited Ryazan while still being a minor; by will of his father he was raised by Vasily of Moscow and later married his daughter) while the first two were officially vassalized as a direct result of Civil War. While before the war both principalities formally (and very vaguely) recognized Muscovite seniority their support of Shemyaka gave Vasily II the justification and means of pressing for formal vassalization (Boris of Tver submitted himself to Moscow and agreed to marry his daughter to future Ivan III of Moscow in 1454; Novgorod formalized its vassalization to Moscow in 1456 by Treaty of Yazhelbitsy) which allowed Ivan III to annex them a generation later
3. While of course Civil War itself wasn’t good for economy and internal stability of Muscovy arguably, the most destructive participant of it was the founder of Kazan Khanate Ulugh Muhammad.
Before 1444-1445 Vasily II suffered several losses, setbacks and prestige hits but his position as uncontested ruler of Muscovy was rather stable after the defeat of Vasily Kosoy in 1436 (there was some power struggle between Vasily II, Shemyaka and other local princes but it was way more peaceful and restrained than 1433-1436 and especially 1445-1453).
However when Ulugh Muhammad decided to participate it quickly turned into nightmare. Tartars pillaged lands all the way up to Moscow, captured Nizhny Novgorod and when Vasily II tried to oppose them his army was crushed and he himself was captured.
When he was in captivity Shemyaka was acting as grand prince (since he was next in the line of succession) and was forced to temporarily recognize independence of Suzdal-Nizhny Novgorod principality. Vasily was able to return to Moscow only with Tartar escort, promised Ulugh-Muhammad a great ransom and was forced to offer Tartars huge land grants (some of which later formed Qasim Khanate). This overt submission to Tartars destroyed his creditability as a ruler. Shemyaka was able to justify his claim to the throne and he managed to capture and blind Vasily shortly after.
The main question is the following: does the lack of Civil War prevent the disasters that followed Ulugh-Muhammad invasion? In my opinion not really – IOTL prior to the invasion there was period of relative stability for 8 years, so even if there is no Civil War altogether ITTL I don’t think that Vasily can amass much bigger force and thus the outcome of the battle against Tartars should also probably be unaffected by the absence of Civil War. If Vasily gets captured as per OTL his prestige would suffer the same hit it did IOTL, this would still create an opportunity for the next one in line of succession to strike his claim to Muscovite throne even if this TTL guy would unlike Shemyaka be previously faithful to Vasily. For most people it is too large temptation to overcome (and it also could be seen as acting for the benefit of state to not allow Tartar puppet Vasily to come back and give Tartars massive ransom and lands) so the civil war of Vasily against the next in line would still probably happen. While this guy could be less competent and less vengeful than OTL Shemyaka in my opinion the changes would mostly be cosmetic.
While one could claim that Vasily avoids captivity because of butterflies (which is of course entirely plausible) allowing to avoid the most destructive phase of Civil War, this would not be a direct consequence of Feudal War and thus might as well be a separate PoD or butterfly.
If the purpose of this thread is to simply explore the consequence of lack of Muscovite Civil War (say because Yuri of Zvenigorod dies before Vasily I) my answer is that situation would probably not diverge much form OTL. Provided that Ulugh-Muhammad still invades and captures Vasily II of Moscow, the latter would lose almost all his personal prestige thus creating a very serious opportunity for internal instability and civil war, Muscovite lands would still be pillaged and Moscow would still have to pay an enormous ransom for Vasily II thus suffering a serious economic decline etc. etc.
If you are however looking for a way to wank XV century Moscow a little bit more I can propose 2 PODs which I would write down in my next post so that this one does not become too long.
