Best to take the mirror out of the cell. Moisture could remain between the cork pads and the glass for a long time, and there is a good chance of mold taking hold. You might want to disassemble the rest of the mirror cell and dry each component separately with a towel and then let dry completely. You don't want your collimation screws and springs going rusty.
The other problem with doing this is that there is usually a lot more dirt and dust on the mirror cell and housing than on the mirror itself which will wash into the water, so you end up soaking the mirror in more dirty water than you otherwise would have.
Same for the secondary. If it has a holder where a clamp is stopping it sliding out, then disassemble and thoroughly dry everything. In the GS scopes there is usually a clump of foam that could soak up plenty of water behind the secondary. It's good to do that anyway to make sure the mirror is not being pinched. Just make sure everything is dry before it all goes back together and it will be fine.
Well that's one way to learn all about your scope.
