Sorry to hear of your situation. I've had injuries happen in classes I teach, as well as classes I've been in . Two of those instances were torn ACLs although neither of them involved the visual spectacle of the leg bent backwards. In both cases the class basically ended there, not our of sympathy or respect, but because the person was literally howling in pain and needed to be taken care of. I think in both cases they got a ride home or to the hospital, in one case the guy called his wife to pick him up and in the other case the woman's boyfriend was also in the class. I had a guy fracture his leg and another dislocate his thumb in my class, and we went on with the class for everyone else (I didn't know the extent of the injury at the time).
You should be able to freeze the contract. As far as the rest, that's up to you. I've only ever gotten "how are you doing" calls/texts when nobody has seen me for weeks, and mind you I've been training at my current place for 9 years and teaching for 6. I hope I don't sound like too much of a dick, but as far as the white belts who I teach (and train with if we're taking the same class), I don't know them that well unless they're serious students who show up every day, and in instances where they have gotten injured I haven't checked up on them while they are out. Then again, I don't run the academy and I'm really more of a student than an instructor.
Take that for whatever it's worth. I wouldn't take this whole situation too personally or let it stain your experience with training. Injuries happen a lot - I've had a few that kept me from really training for several months at a time. Veteran instructors are used to seeing their students get hurt, and if they're not personally close with that individual I wouldn't expect too much contact.