How to (possibly) survive the abyss, by Jim:
1. When you arrive, eat your food if it's safe to do so. Don't get caught hungry. Switch to gear that includes MR if possible. Levitation is also nice.
2. Keep moving at a slight angle. That is to say, go left 3 steps, then down-left and repeat; this covers ground expediently.
3. Do not stay and fight. If you see a Pit Fiend, move in the opposite direction if possible and try to lose your pursuers. Use the walls to your advantage. Fight only when it saves you time to do so. The longer you stay still, the sooner they'll close in from all directions.
4. When you inevitably get hedged in, teleport. It may take a while to kick in, so do what you can to stay out of LOS for smiters / hellfire-ers in the meantime. Remember that blink is almost worthless in the abyss. Keep your eye out for the portal - or rune!
5. Scream "Day shall come again!" with each sword stroke as they crowd in upon you. Die a heroic death.
6. (optional) If you find an altar to Lugonu, converting gives you the ability to instantly depart the abyss.