[EricH]

I think both posters need to have a heart-to-heart with their mentors. Take the mentor off to a quiet corner of the shop for a few minutes, and talk over how he's feeling, how the team is currently doing, and things like that. Then bring up:

Mentor A: You've noticed that he's really starting to wear thin (break down, be overworked). How can you help? Maybe persons X, Y, and Z are ready to help take some of the load off--but he has to let them. Which of those does he trust to make the right call if he is taking a much-needed break?

Mentor B: The team is having a hard time doing work because his schedule (or other valid excuse) doesn't allow him to approve stuff getting done fast enough. Which other mentor(s) would he trust to make a good final decision in his absence, and could he convey that to those mentor(s), as he knows he won't be there forever?

By telling the mentor privately that you've noticed this, and maybe he should designate a "proxy", you've shown that he doesn't have to run the team alone, or make the final call himself; by having him choose who the proxy is, he can choose someone he trusts to cover for him if he just needs some R&R. And, by the same token, you've shown him that you care about his well-being, as much as he might care for the team's. And by emphasizing the "in absence" part a little bit, you point out that a) this is only for when the mentor isn't there and b) the mentor might want to take a little more time off, knowing that the team is covered by another mentor.