For the option, of course all of us would love him back.
I'd even be OK with overpaying him to stay on a 1-2 year deal that would have him expire when Pierce does.
However, we absolutely cannot give him a ridiculous 4-5 year deal as some other team will likely offer him.
He's a very nice player, but most of his game comes from the open looks he gets due to the attention that the Core Four draw. The same thing happened to Big Baby, Posey, Shaq, and other who have been the 5th man on the floor with them the past 5 years.
If JaJuan Johnson continues to develop, I see no reason why he can't do many of the same things that Bass does. Like Bass, he can shoot our to 18 feet or so; like Bass, he can finish at the rim; and unlike Bass, he looks like he could be a shot blocking presence.
So again, I love Bass, but he's replaceable. I hope Danny doesn't do anything silly with him.