I got to the nether for the first time, promptly saw a ghast, and started running away from it. The game suddenly crashed and closed completely. On reloading the game, I was back in the nether, but I couldn't see my portal. I assumed I'd run a bit away from it when I saw the ghast, so starting looking around. Half an hour later I still hadn't found it, so I fired up Minutor to help my search.
I set up a colour scheme where lava, netherack, gravel, soul sand, fire and bedrock are all alpha 0. Obsidian and Portal are set to bright green, fully visible. It seems from this map that my portal has gone completely. I checked at a variety of depths, just to be sure, and there's not a trace of green to be seen.
Is it possible that my portal has disappeared?