Well if we sign Hayward one of Kelly (renounced), Crowder traded (plus smaller pieces), or Bradley traded is required to get the max cap space. So if you renounce Kelly, and trade Crowder by himself along with possibly picks it makes it tough because his salary is low. Maybe someone like Favors but there won't be a ton of options. You could trade Crowder for a future pick to clear cap space, and keep and start Kelly. Maybe Kelly would play better in the starting lineup, and be less inconsistent. Who knows. You could just renounce Kelly and start Crowder as a small ball 4. You could trade Bradley, my least favorite option, and start Hayward at the 2 alongside Crowder and Kelly.
If we miss out on Hayward I don't think it's the end of the world. You could either work towards extending Thomas and Bradley, or even Smart for that matter. Or you could use that cap space to upgrade the Amir, Tyler, Jonas group. Maybe split the cap space between a small ball 4 like Gallinari or Gay and a big like Randolph. Even then we would still be in the mix for ECF, and Lebron will be another year older. Especially if 1 or 2 young players break out like Brown.
Big picture if Ainge plays his cards right we could arguably have the best young core 3 or 4 years down the road (with a few other teams in the mix like Philly, Wolves, Bucks), as many of these stars now on the best teams enter their 30s, and on the decline.