Will the duration of the delay depend on the damage/method of destruction?
Like Delay 1 per point of damage prevented?
Nope. Destruction is 1 turn delay.
Eaten , reduced to 0 hp, Paradoxed, etc, all cause the creature to be delayed 1 turn instead.
Shockwave is the intersting one if the Undead is 4Hp and Frozen. The damage will kill the creature causing it to be delayed with 1hp, then the kill effect will cause and aditional point of delay.
Regen I sounds awfully similar to this ability in this other game I play...
Regen is common in many games. Its been swapped out for just healing because of competition requirements.