But that would be illegal - I was initially thinking of this as a joke in the replay, but then I realized under US law at least this would be a crime.

To be clear: a company can arbitrarily break something you paid for by terminating your account, or just taking the servers online, that is completely legal. That company can then sue you if you connect to someone else's servers or bring up your own, because that is illegal copyright infringement or contractual violation (and possibly CFAA violation because idiocy).