Hi,
sorry, bad news, I would say. Since drive D: is critical due to the tombstones stored there, it cannot be removed via console, amd it's missing will affect server functionality heavily. Is there anything in the event log, which could explain why the drive did drop from the storage pool?
I had the same one time, in that case the file system had a shot. What ever I tried, no chance to repair it. I also had finally to perform a server reinstall, which I usually avoid as long as possible.
You could try to perform this reinstall to a new system disk keeping the old drive on side, or on the same drive.
If you do not get a server reinstall offered, you will have to go the hard way as described in the FAQ How to recover data after server failure.
Best greetings from Germany
Olaf