... if Rose had not returned?

I mean, he had no TARDIS, no apparent means of escape and was on the verge of extermination. However, he had three regenerations left. Would the Daleks just have waited for each regeneration to complete and exterminated that too?

I had always thought that regeneration was triggered when the Doctor was on the verge of death rather than dead. If he was killed instantly, he wouldn't have time to regenerate. Then the TV movie came out showing the Doctor dying and not regenerating until several hours later, but there quite a few things about the movie that didn't quite tally with what had gone on before.

Maybe he would have regenerated into something that was immune to the Dalek gun (who knows how Gallifreyan evolution works?) - in which case it's a shame Rose came back when she did...