No matter who purchases your company to begin with it is all who the company admin is.  An accountant could initiate and set up your company for you but never add you as a company admin and they could even lock you out on their own (perhaps if you did not monthly reimburse them for their wholesale billing) but you as company owner own the data. It is under your control to remove (uninvite) your current accountant user(s) at any time.

Your data does not go anywhere, even if someone stopped paying for it for 364 days it can be reinstated to full service before day 365 from reports only.

What happens, whether you are changing accountants or simply taking over payments is that the accountant user will relinquish payment status back to the company admin (you) and the payment method that you have on file with Intuit. If you have none on file then the subscription halts after 30 days and becomes read only for that aforementioned year. As long as you have a valid payment method on file then there will be no skipped beats. You can even have a new accountant user provide their discount rate once you select a new accountant user.