But, what about resigning when your opponent is very low on time and has winning position?
If your opponent has miss-handled his clock, that's as serious an error as if he had blundered away a piece. Time is a resource, just as material and position are resources. The opponent may have a winning position BECAUSE he spent far too much time on the early part of the game.
Short answer: No, you are NOT expected to resign just because your opponent has messed up his handling of the clock.
Resigning is as much a matter of respect for yourself as your opponent. I don't feel disrespected if a player tries in vain to stalemate me. If they're happy to keep playing with only their king then I'm happy to extend their false hope. If a player wants to try to win on time from a losing position there's nothing wrong with it. It could work out to be good practice for both players.