At the very least I'd hope he resigns - surely a second GE defeat would make him realise it's time to go.
Keir Starmer seems a decent replacement, because Labour must re-position themselves more towards the centre in order to give normal, decent, proper Labour supporters a party they can support, rather than the rabid Marxists currently in charge. Whether this would be possible considering the jack-booted Momentum clowns who are currently pulling the strings, remains to be seen.