Changing a cats diet

Our town recently had one of our vet offices close for retirement and all the in town and surrounding areas vet offices have filled up and they are no longer taking new patients. I have a 14 yr old male cat that has been on Royal Canin SO dry for probably 13 yrs and his prescription at A is good for about 8 months yet. What I would like to do is to change him from RCSO dry to a quality non prescription wet cat food. Can this be done? My concern is that he gets sick and I will not have access to a vet to treat him. Any help/suggestions would be greatly appreciated. Thank you.