I really think the Cavs need to make this work more than Boston does. Without this deal, there's no way (IMO) that the Cavs can find a deal where they're both 1) at least close to as good as they were last year, and 2) acquire a phenomenal trade chip (the Nets pick) that can either be used to snag a star player to help entice LeBron to stay or to draft a future star that will ease the post-LeBron transition.
My prediction is that the deal still gets done, with either no changes, or the only change being a second round pick thrown in by Boston.
If the deal doesn't get done, Cleveland then has even less leverage when it comes to Kyrie, as the season is now even closer to starting than it was before, and the potential trade partner with the best assets in the league (Boston) will no longer be an option. There's no way the Cavs can realistically expect to find another offer that even comes close to ours.
If the deal is voided, the biggest issues for us are that IT and Crowder may not be too excited about returning to Boston. As for IT, I love what he's done in Boston, but he'll be fine. First of all, if the rumors regarding his injury are true, he wouldn't be playing in a game for at least another 3-4 months (if not a lot longer), and time heals all wounds. Second, he has no choice but to suck it up, try to have the best season possible for us and set himself up for the biggest payday possible next summer.
Crowder may be a bigger issue, as his contract isn't expiring and he's proven that he's sensitive in the past. If Ainge/Stevens feel that him returning will present a problem, we ought to be able to include him in a package along with one or two of our own first round picks that nets us a pretty good player.
In the long run, we may end up winning fewer games this season and/or not advancing as far in the playoffs, but we'd have the Nets pick back in our arsenal. Our future is bright either way. Cleveland's? Not so much.