Really depends on how bad the resorption is and what level it's at. I think if totally in bone and not too advanced, should try RCT first. But if involves suprabony area, most likely need extract unless can do RCT and crown lengthening to restore area. But there is no guarantee that such a RCT will work, so, warn your patient first.
For ext resorption,try n remove the causative factor first n then do rct , u might have to do apicoectomy with reverse filling sometimes ...n at other times the only option left is extraction..