To be fair, the 'Sim City' guys could just make a new company and continue with a 'spiritual successor' to Sim City.
Saying that, were any of the people from the older Sim Cities even still working at Maxis anyway?
I dunno, whilst I do like specific studios, the developers move around quite a lot.
Look at Rare. The guys who made all the good games left and went elsewhere pretty much after Microsoft bought them. Rare hasn't been Rare for a long time so if they closed down, nothing of worth would really be lost.