I have seen this happen twice at a smaller scale. Turnover is too high quantitatively and qualitatively to survive by hiring new people, so Musk's "solution" will probably be to oursource a lot of stuff to some consultancy firm. Twitter will almost inevitably rot within 5 years. But don't expect anything noticeable overnight.

Edit: also the reason Musk wants to shut down all those microservices has nothing to do with money, it's that he doesn't have enough manpower to maintain them. If Twitter is like most non FAANG out there those "microservices" are coupled with each other, so good luck.