1.) Yes, they did. However they didn't leave. Did they?
2.) He's stuck? Did he not lead Cleveland to 4 straight NBA Finals? I agree, he didn't get a lot of supporting cast, no doubt. I'd say had Irving stayed, the series would more than likely extended a few more games.
3.) We can play the "what-if" game all we want. I would not put the game 1 loss solely on J.R. Smith. Yes, he made a bone head mistake. But let's not forget that George Hill missed the second free throw attempt prior to Smith's mishap.