So I have a 1999 s70 and the motor is done. However the ring gear is also gone I was just wondering if I swapped the motor like I was planning to would that fix the ring gear or would I still have to replace it?

May sound stupid but I'm learning here so

 

When you have the motor out you will have to still replace the ring gear on the torque converter (automatic transmission) or the flywheel (Manual transmission) unless they just happen to be included with the new motor, but that is highly doubtful. If you have a manual transmission, I would do a clutch job at the same time while you have it all apart.