Numion said:
I say nay!
Immortality should require a heavy sacrifice: lichdom, vampirism, etc..
If you can pop longevity potions whats the point of becoming a lich?
I said yes.
The ancient wizard who loves some form(s) of physical pleasure too much to give them up using magic to extend his/her life, is a fantasy staple. Especially if it takes the form of some deal-with-death-unholy-bargain.
My chioce in campaign flavor right now is that there should be options than just more and more undead. Why make life too easy for the PC's?

After all, the undead "heavy sacrifices" come with little flags to tell the players "I'm Evil (pronounced eeeee-vil)! Kill me for the XP!"
Iron Monkey said:
It is not 99 separate 1% chances, it is a cumulative 1%/potion drunk, so your 99th potion has a 99% chance of undoing all the effects.
The question of drinking your 99th potion presupposes your succeeding at your previously succeeding at 98.
Starting with a 1% failure rate, this first potion has a 99% cahnce of succeeding. The second potion has a 98% chance of succeeding, presupposing that you made the first role, for a total probability of (0.99x0.98) 97%
The survival chance for you surviving by the time you get to your:
fifth potion : 91%
tenth potion: 86%
fifteenth potion: 28% (.99x0.98x0.97x0.96x0.95x0.94x...x0.85)
This drops off a lot more quickly than you might think. Consider once you get to about ten potions that if you round off the odds of failure as 1/10 instead of 10/100, the odds of rolling three, four, or even five ten-sided dice without rolling a one gets lower and lower.
twentieth potion: 10% chance that you survive this long
twentieth-third potion: 5% chance that you survive this long
The odds of getting to the ninty-ninth potion are one in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000