C-41 is a four-step process: Developer, Bleach, Fixer, Stabilizer.(posted 8656 days ago)There is no recourse at this point for the development stage, and who knows what C-41 bleach does to B&W films, but T-Max films require longer fixing times than others and they need a thorough wash to remove the purple anti-halation backing. If the negatives are purple, I would wash them to remove the stabilizer, refix, rinse, treat with Perma-Wash or Kodak Hypo Clearing Agent, and then do a final wash and see how the negatives look.
At least they should be properly fixed and cleared.
Compare the negs to negs you know to be properly processed. If they are thin (sounds likely), and they are really worth the effort, you might get some improvement by treating them with Selenium Toner or Chromium Intensifier. If they are too dense (I doubt it, but who knows?), you might try a reducer. Of course you will never get back detail that's been lost, but you might get more printable negatives.