I think Trump dodged a bullet with this one, even if he did originally fire it at himself. By most accounts, Flynn was a fine general, but was in over his head management-wise as Director of the Defense Intelligence Agency.
Whatever Flynn’s relations with Moscow might have been — and I suspect they were overblown — the President just can’t afford a bad manager as his National Security Advisor. Better that Trump take his lumps quickly and appoint someone better qualified for the job.