This is a bit premature. If and it is a big if a nefarious corporate entity was to purchase an instance, then magazines would be re-established on other instances and so would users. The instance would effectively die off and be reborn elsewhere. For most people I sense this wouldn't be an issue as the cost of moving instances and creating new accounts is generally quite low.
If you are concerned around the possibility though, you can always set up a new single user instance, which you have more control over.
To be honest, the only reason to move accounts at this point would be if the instance administrator asked - due to issues with load, for example - in order to be a good citizen. Until that time, try not to worry and enjoy the fediverse 🙂