The thing that gives me optimism is that in Conte we are getting a proven winner and force-of-will manager in his prime. Even if he stays with us for just the 18 months that his contract is for, he will have instilled a completely different mentality in the club and players; one that even Poch couldn't instill. After that you can bring back a Poch or go for Potter and the aftereffect of the Conte reign should carry through and allow them to be successful. Keeping him for an extra year would reinforce this even more.
The other area Conte will impact the club is in the transfer market. He is going to "force" some signings that will improve the team that another manager might not have had the clout to force. And he will probably make it easier for us to sign some of our targets as he would likely be a huge draw for said targets. Couple that with clearing out players with the wrong mentality and whenever he ends up leaving he will have left a much stronger squad and tougher mentally. He did that at Juventus and he did that at Inter. No reason why he cannot do it here too.
All in all, this is a win-win for now and for after he's gone, unless our players are really beyond salvation, which I don't think is the case.