Unfortunately no one except perhaps the company itself will be able to let you know the probability of you getting an offer. I have seen quite a few people on TSR speak about getting an offer from the waitlist, from a range of different companies, so it’s not uncommon.
Graduates reject their offers because they get multiple offers, or have changed their minds about the role - all the time. Which is why companies have reserve lists. So it’s definitely possible, but it depends on how many graduates reject, and how long their reserve list is.
I would keep applying to other places as normal, accept suitable offers elsewhere, and if this company does come through with an offer, you can make your decision then. Good luck !