When I was DMing 1e in the 80's, players in my group would simply retire a PC that got zapped with multiple level drains. They then would make a new PC of the lowest xp total of the remaining party members with minimum starting gear. Generally, until characters could recover lost levels with restoration, death was easier and more preferable than being drained of levels.
Sure, encounters with level-draining undead were exciting (vampires and specters drained 2 levels per hit, no save), but in the way a drunken night out is exciting. When the party is over, there is remorse and sickness.
Even more problematic than how level drain messed with my campaigns was the extreme meta-game nature of the effect. An undead drains your life force, which is represented as your level and experience points . .; . so, it really ended up being "memory drain", except only memory of spells, combat tactics, and skills. Huh? Draining of life force would have been better accomplished by ability drain (as noted above), or some other effect, such as % of hit points.