HCA: Hermit Crab Association

I have a medium-sized crab named Dewey, who dug down in the main tank on December 15th, 2023. His cave was built against the window so I could see him but I never saw him molt. I covered the window to make sure he had plenty of darkness and peaked at him now and then through the window but it seemed he never molted.

Then in mid February he started crawling around. I could hear him crawling through the sand so I assumed he was coming back up. But after two days he still hadn't resurfaced. On a side note, I was also worried about another crab named Snowball who had been down way too long (almost 6 months), so I carefully dug him up. Unfortunately Snowball had passed.

So I removed the deceased Snowball and moved Dewey to an isolation tank with deep sand. Before I put him in the isolation tank I gave him a brief bath and let him crawl around for a bit to dry off, so he would have gone down with some water in his shell. His exoskeleton showed no indication of a recent molt. He dug down right away and I haven't seen him since. So basically, he has been buried in the isolation tank for 7 weeks. But keep in mind, he had also been buried in the main tank since December 15th. I am worried that he has been underground for so long now that he must be very depleted. I don't know if he is now molting, or if he already molted and just feels like being under some more. Or he has died.

What should I do? How long should I wait before I gently check on him?

I would wait at least 4 months. Even if he is depleted from being dug up and moved, digging him up again may cause even more harm. If he's already dead, there is nothing to be gained by digging him up.
They know what they are doing when they dig underground, and it's best for us to let them do it and not mess with them.

Curlysister, thank you so much for your thoughtful response. I will wait. You're right, he's either dead or doing what he needs to do. And if he is sick in some way, there is not much I can do for him if he is choosing to stay underground. Just have to wait and hope for the best.