The standard line is usually that any money left in a local unit's treasury goes back to the state PTA; that's why most people find ways to spend their funds down before they switch to PTO. However, you need to check your bylaws. They should address specifically your question, as well as the procedures necessary to dissolve your group.
We are a school in New York State and are switching to PTO. Can anyone tell me what we do with the funds in our treasury. Are we able to just continue using them or do they in any way belong to PTA?