Like Glorious said, it's a hypothetical. If the solo was prevented and resulted in a stalemate where Germany and Turkey held critical SCs, obviously it would have been a 6-way draw. If there was an option to safely eliminate Germany and/or Turkey, I'm honestly not sure what I would have done since they both switched sides during the endgame. If the game went on and they worked closely with us and were integral to stopping Russia, I probably would have pushed to keep them in the draw. If there was more back and forth of allegiances, I probably wouldn't defend them.
If for some reason it was E/F/R/I left standing, I am confident that I would not have allowed Italy to be eliminated from the draw, unless somehow pretending to go for an EFR draw meant I could stab France and Russia enough to have the chance at a solo myself (not so likely, but we're talking about hypotheticals). I'm not a sentimental player and would stab a game long ally if it meant I could take a solo, but the difference between a 3- and 4-way draw is marginal. Italy played a crucial leadership role for our coalition and was a valued partner to me throughout the game. We developed a strong rapport and he had my loyalty. I'd also have used my military and diplomatic leverage to protect Italy from France if France was tempted, although France has made it clear that he also grew to value his relationship with Italy, especially in the endgame.
I'll defer to you guys on the tactics of whether Russia could have locked in his position and prevented us from pushing him back had he not reached the solo. This was my first experience with a hard fought endgame, so I don't have much tactical knowledge to draw on. *If* it would have been tactically feasible though, I think that the E/F/I alliance would have had the trust and close coordination necessary to roll Russia all the way back. Once we were in the endgame, I would have preferred and E/F/I draw to and E/F/R draw given our very close cooperation and rapport, but an E/F/I/R would probably have been more likely.