Given the small majority the government have, there's little chance that Cameron could survive a vote of confidence. After that, there'd be riots if a general was not called quickly.
Pretty well the only thing the Conservatives could do to lose the next generation is to elect Johnson as their next leader. It's most unlikely that they will do so, although they did manage to lose the 2005 election by giving the leadership to Howard. I reckon they've learned from that and they have dozens, if not hundreds, of better candidates.