Whatever happens for the next few months after the division has been anounced, Hyderabad will continue to remain the state capital for Telangana as well as Andhra Pradesh.
The parliament will be shared by the two states. High court might continue to be same for at least two years, till Andhra Pradesh high court is built. Also there will be immediate need to form Telangana Police Force.
After 10 years if, at all, Andhra Pradesh can build its own brand-new capital, yes, AP can change its capital to the new city.