So this is what I think about Boston, assuming game 3 was a last gasp and not the start of an amazing upset:
Go hard after Hayward. If you land him, then move the #1 pick this year and some other throw in stuff (hopefully not next year's Brooklyn pick) to add Butler. Thomas/Butler/Hayward/Horford is a core that can compete. Re-sign guys as you can.
If you don't land him, draft Fultz, avoid the big trades. Neither Butler nor George alone is enough to compete. Then make the incredibly hard decision next year to let Thomas walk. Really small guys tend to age terribly, get out, hoard cap space with Fultz, Brown, another likely top five pick next year, etc, wait out LeBron a bit, etc. Team should still be really good next year, and maybe avoid ever really rebuilding while having a much better shot in 2023 or whatever.