I think Mastodon will survive. Other fedi projects (eg. Pleroma-fe) have been through all nine circles of FOSS hell and somehow still ship usable builds to a sizable community.

Eugen's presence is felt and appreciated in the community, but I can also understand why he stepped down. It's hard to represent so many people who don't always agree with you. I think back to Jack Dorsey's final days at Twitter with the NFT profile pictures and crypto tickers - he truly did not understand that his leadership had passed it's prime. The honorable thing for him to do was pass on control to someone responsible, but instead he spent his final days polarizing Twitter and guaranteeing it's own critical insolvency.

Eugen took the honorable route - I hope he remains vocal and influential in the community. It sounds like he knows himself extremely well and I applaud his honesty about the temptation for ego to ruin big projects. Most of us can't imagine the pressure in his shoes.