I think he deduced the only way to defeat the Daleks would entail destroying the Timelords as well, so he scarpered. I'm not sure whether he had any long term plan or not but presumably he envisaged being the Master again.
Given the Master, Davros, the Emperor, the Cult of Skaro, the Dalek from "Dalek" as well as a whole heap of other Daleks survived the Timewar, I still find the notion that no other Timelords survived unlikely. If Moffat or another showrunner wants to bring them back he (or she) will, irrespective of Time Locks, moments or anything else...
It's kind of amusing how all the bad guy's somehow fell through the cracks at the end of The Time War but all the good guys or as good as The Time Lords could be were wiped out. That's why I think a small group of them escaped and rebuilt Galifrey in secret.