Aside from the implausibility of holding Austria off for more than a February and the summer without Napoleon (hey, improbable things can happen),
May you explain why? In late 1799, the military situation was in fact improving. Brune had defeated the British and Russians at Castricum on October 6, and the Russian invasion ended at the Battle of Zurich, won by Brune on September 26. Without British and Russian help, Austria had no chance to enter France (as "holding off" suggests). It was now necessary to take back Italy. But Napoléon wasn't the only one who could have won the 2nd Campaign of Italy, since France had many talented commanders (even if Napoléon was arguably the best of them). In fact, Napoléon's Italian Campaign of 1800 was only possible because, at the same time, Moreau fought against the Austrian forces in Germany and defeated them at Hohenlinden. France could have won this war without Napoléon.
To quote a French saying: "The cemeteries are full of irreplaceable people".
A console system of requiring unanimous agreement among the three might form (you can guess how often nothing will be done with this).
Here, you are confusing two different systems. Sieyès' original proposal didn't mention three consuls. Sieyès imagined that the head of state (the Grand Elector) would appoint two consuls, one for foreign affairs, one for interior affairs. No agreement is needed between both; and if they aren't cooperating, the Grand Elector can dismiss them at any moment. The Consulate with three consuls was only created when Napoléon rejected Sieyès' system. Indeed, Sieyès' proposal didn't provide a place for Napoléon. Grand Elector? Napoléon didn't want to stay a passive actor. Consul of foreign affairs? He could have commanded the armies, but he could also have been removed from office. Sieyès' system wasn't suited for a dictatorship. Thus, it was agreeded to abandon the Grand Elector and to replace him by a First Consul, with the two remaining consuls only being his counselors and deputies.
once the situation settles down, I don't think there will be a Napoleonic Code.
The Code Civil (or Code Napoléon) was enacted under Napoléon's government, and Napoléon indeed accelerated the redaction of the law. But the text itself was the work of Cambacérès and of a commission of jurisprudents. Sooner or later, the French government will create a civil code for France, with or without Napoléon.
I can imagine reworking of the public code, but it might more be tweaking the existing system, just as some people proposed amending the articles of confederation to work instead of starting form scratch.
Again, please explain yourself. What is the "public code"? The constitution? Well, a new constitution would have been enacted -- it happened in OTL after 18 Brumaire and it would have happened ITTL. So yes, the "public code" would have been reworked. Speaking of codes, one code might survive: the 1791 penal code. This was a very liberal law (the legislators even almost abolished death penalty in 1791), but was replaced by a more reactionary one in 1810. For example, the 1791 code had abolished branding and life imprisonment. These punishments were reintroduced in 1810. Clearly, Napoléon was more conservative than the revolutionaries of 1791.
On review, this topic has been discussed
recently;
@G.Washington_Fuckyeah has great posts on this.
I didn't answer to your original post because I already wrote quite a lot in the thread you linked. But if you have any questions which haven't beens answered there, feel free to ask them in the current thread.