In my case the other day I was stuck between floors, so no escape through the doors. Incidentally, when the power failed the doors automatically opened about a foot and released, presumably so you could make an easy escape if you happened to be near a level. The manhole escape hatch was however more than 3m above me, and had a key lock on it. Nothing to climb up on except one hand railing on the far side of the lift. So I just sat tight and killed time by surfing the web.
The other lift next to it has an unlocked manhole you can reach with your outstretched arm. So if I was in that one I would have climbed out myself and tried to prise open the outer doors on the upper level. That would be a silly option in the pitch dark of course (no emergency lights), but I had a torch with me.
Dave.