If I had to guess, and I'm seriously just guessing here, trying to perhaps think along Tolkien's lines, then I sould think Orcs were corrupted to be polar opposites to Elves.

they would love no craft, find nothing beautiful, have no compassion or empathy of any kind. Their lives would be short and brutal, and they would preserve nothing. What's likely most important, is that they would literally have no souls, no will or power, being little more than cunning animals, easily lead or duped, fearful and reactionnary. Given those parameters, I'd think that Orcs who died would simply rot, no soul would journey on, but rather they would simply return to the earth to which they were tied.

I would not think they would be sent into torment after death, since in the end, their lives were not of their choosing. Tolkien was generally one for forgiveness and the redemption of those who were wronged, so it perhaps fits that Orcs would be allowed to just die, and perhaps find some peace in that.

Returning to the halls of Mandos might have been the fate of the first Orcs, those who truly were ruined and corrupted Elves, but again, all of this is conjecture.