Descent into Hell!!! Rarrr!...Well, sort of...

[HerenIstarion]

Is this hell in ME eternal as well

In two different ways, yes.

In time: Self-withdrawal from Eru, if unrepented of, seen in retrospective, is eternal. So, unless he repents, Sauron is always damned. If he repents, than the time previous to repentance may be seen as the ascend to the culmination point of the repentance and bliss, and therefore also eternal - once blessed, he would have been always blessed.

Outside time (Void): self-explanatory, I reckon - the 'place' is outside time, it is eternal.

The revert of the concept of Christ's descent into Hell - by this Act, He releases pre-Christian prophets - i.e. the Act goes both ways in time. Another point of view for the same Act - it is eternally performed, for God is not bound by time, and Christ is descending into hell to release every moment of the past-present-future consequence, which is consequence at all from human point of view only.

See this