I honestly wouldn't be too shocked if this happened, if its for health reasons, living situation reasons, or just pure disinterest in hololive, it seems clear to me that Gura just can't be a streamer anymore. Now i fully believe cover would do anything in their power to keep Gura on board, she's worth vastly more as merchandise and a mascot than a streamer. But if anyone in HoloEN is likely to leave, i agree with the redditor that its gura I'd put money on.
Now I don't think Gura leaving would be a massive impact to Hololive or even HoloEN, you'd 100% have some drama and some fallout from it, but all of HoloEN would bounce back pretty quickly. The Biggest hit would be to Hololive merch, as now Gura is pretty much unusable given her departure, and they'd need a new face for HoloEN.
For the record i don't really think Gura will graduate, i am still firmly in the "too big to fail" or i guess leave camp, but stranger stuff has happened.