Well, apparently having a good regular season and then falling off in the playoffs has been Bass' M.O.. Happened in both Dallas and Orlando.
I think with how little most Celtics' fans knew of Bass, this ended up being overlooked. Everyone just assumed since he played so well in his role during the regular season, it would continue in the playoffs. I am guilty as well.
Ultimately, this is partly why Bass is best suited to be a backup PF. Relying on a one-dimensional player eventually comes back to bite you (not that the C's had much choice).
As far as retaining Bass for future seasons, I think it depends on dollars and role. I do not want him back at big money or as a starter. As a bench PF for similar money to what he was making this season, I'd take him back.