Mri showed tfcc tear where blood supply is poor. 3 months later with splint and cortisone pain is gone. did it repair itself or is tear still there?

Probably healed : It is most likely healed but occasionally pain may diminish with time without healing due to other factors. Only a repeat MRI will likely reveal the truth.

Good question: Tfcc tears are repairable. So, o\if your treatment rendered a normal wrist there is probably a good chance some or all of the tear has healed. Continue to strengthen and time will tell. Good luck.

Maybe?: Tfcc tears can take a long time to heal and sometimes do not heal. Cortisone could be masking the pain despite a persistent tear. I would probably just wait things out and see if the pain comes back. No need to do anything else unless the pain returns.