Maybe I'm wrong but I don't think it will be particularly close. Butler/bam may play better and be more aggressive but these game 7's generally come down to what roleplayers show up. And roleplayers usually do better at home.
Think one or two of grant, brogdon, white, smart, Horfords has a big game.
Celtics shot 20% from 3 game 6. I expect that they wat he's the tape and realize they got away with one in game 6 and will come out out high energy with better ball movement