Just curious - any of you (or your managers) ever had to fire a DBA? What were the circumstances? I don't mean lay offs.

To me, "human" errors (to put it politely) that significantly affect revenue (due to down time) are simply unacceptable. You hose a database with 5 users due to negligence, I might let it pass. If you hose a database with 500 users and it results in downtime of a day - adios.