My insurance company has given preapproval for radiation which is on going and i have quit my job..?

My health is covered by the company which i work for. I have cancer and the preapproval for radio therapy has been given by the insurance company. I am midway in my radiation..ie.. 4 weeks done and 3 more to go. Inthe meantime , i have quit my job...will the insurance withdraw the money already paid to the hospital?.Is the money paid to the hospital in advance for the treatment or is it paid later?