I'm not sure you answered the question so I doubt it was helpful
.
Inverts can be very sensitive to temperature and water quality issues.
While there is no guaruntee that it will survive, I wouldn't count him out yet. I have seen brittles bounce back from some pretty extreme issues. For myself, my heaters failed during an usually harsh winter and my tank was on a sun porch and dropped down in the 60's before I was able to slowly bring it up and inverts were all that survived, after a rough period though.
I would leave it be. Do you have a cleanup crew? If he should die, you will see body, starts with the legs, but actual body deterioration first. Then you can either choose to remove him or let the cleanup crew do it's job. A lot of this would depend on where it's located, how old your system is, and how large the system. A larger, more established system is more likely to not suffer any water quality issues over a death in the tank.