Well, there's always the Fifth Amendment, right? You take the stand, repeatedly invoke the Fifth, and you go home. You won't have helped Burge at all, but you won't have put yourself in harm's way either. That's exactly the course a good number of Burge's former officers want to take.
Here's the problem with that: Because you waived your right to take the Fifth Amendment when you testified in the civil suits, it's not at all clear that you can jump on that rescue vehicle now.