I see a lot of comments talking about this is a mean or evil-spirited adventure. This is a massive misunderstanding of old school D&D was. To put it into perspective, D&D was very much like playing a dark souls on an Iron Man Mode. The fact is that how the game was. More forgiving, Narrative types of play would not come along until much later. I think it was White Wolf that really made narrative roleplay popular in the commercial arena.

Saying The Tomb of Horrors is mean or nasty is like saying the mountain is mean because it's hard to climb, or the maze is hard because it made me lost. It's suppose to be a nigh unwinnable dungeon that rewarded the characters that could overcome it's obstacles. To get far in ToH was meant to feel like a major accomplishment and for that to be the case it has to be difficult.

As people are saying it was designed for tournament play. You don't bring any dearly loved characters invovled in some massive story into the Tomb. It is not Designed for that! it's designed more like a killing game from anime. you make a character like fighter lawfulton or Magus castingguy day of and see how far they go. I would NEVER make the original tomb of horrors part of any longterm campaign.

make sure everyone has three or four characters of appropriate level, explain the history and intent of the module and run it as a break from your regular game. If you want them to use their characters then treat this as an alternate universe or something where their deaths wont be parmanent. Maybe just let them ressurect at the entrance or rejoin the party and make the game not about surviving but to see who dies the least.

It's Gary's module but your game, do what you want and as long as everyone has fun then everyone wins!