National Acrobat:
I notice no one has posted a suggestion something like the following:
Let the dice fall, yes.
If a TPK happens, a TPK happens.
BUT...
LET THE PCS ENJOY THE AFTERMATH OF THEIR HEROIC DEATH IN THE NEXT CAMPAIGN.
You said that some of them know that they will die, but their characters don't.
THAT IS NOT SUICIDE, IT IS GOOD ROLEPLAYING.
If some survive, let them hear, at the next inn they go to, the Ballad of the Heroes, where a bard sings of the PC's heroic sacrifice, and their glorious death.k
Have people on the street be talking about the Heroes who fought the Drow. Sure some of them may have died, but now the common folk of the land worship them.
If any of the PCs survive the fight by some miracle, have the common folk treat them as gods: "You want to give me the honor of staying at my humble inn? You can have the finest rooms and the best food for free! It is a small thing, compared to what you and your fallen comrades did!"
or
"You want to buy supplies at my store? You can have them at no cost! May the gods be with you!"
or, somewhat more pertinently:
"You have honored my temple greatly by coming here! I shall ressurect your fallen friends forthwith, and don't worry about donations! One cannot put a price on such great sacrifices that you have made!"
You get the idea. Let them enjoy the fruits of their heroics.