If one of my testicle atrophied from infection a decent amount, is it possible that the leydig cells are still left in it and only the sertoli died?

Possible ...: The destructive effect onto different cellular lines from inflammation (orchitis) may widely vary so the degree of resultant damage to different lines of cells will differ. But, as previously discussed, the bottom line is still the remaining function after inflammatory disaster of infection; to prove it, testicular biopsy is needed but probably not clinically necessary.