[thejeff]

It's also pretty uncommon in a normal assassination to not have one side or the other dead or fleeing long before turn 50.

It would be a pretty odd situation. You'd need to be completely invulnerable to your enemy to last long enough. And he have to be invulnerable to anything you could equip yourself with or why bother.

Knocking yourself out with your own aura probably won't work, since you'll hit 200 and start taking damage.
A berserk, blinking assassin with 2 Life Long Protections and very low movement (crippled?) might stay out of the way long enough to trigger the defender's route even if the imps couldn't scratch him. Probably wouldn't work, but it would be fun to watch.