You've received a lot of good advice so far. I just want to add an anecdote from my own past:
I was in a band. We started to feel like the drummer wasn't up to snuff. He was a nice guy, but it seemed like his timekeeping wandered a bit. Nobody noticed but us. We fired him. Then started looking for a new drummer. We never found one that fit. The band broke up.
Now, the band breaking up was partly due to other factors, but firing that drummer when we did meant we didn't get to play out or enjoy the experience of being in a band.
I'm not saying you shouldn't replace your bass player. Just be very, very sure it's the Right Thing To Do.
You don't work music, you play it.
Discipline is not the enemy of fun.