If he bought them through school he got a hefty discount. Most are right that 50% of new is a rule of thumb for buying used tools. I would bet that is about what you get back if you turned them over to SO.
It is not as easy as just turning them back in and being paid off. They will work it out with you on a value of them. It maybe enough to pay them off, it might not. Really no different than turning in a car you have financed, the value has to be more than owed.
I would contact the school and get the SO contact person that sold the tools originally. You are not the first student this has happened to. Most of these guys have actual dealers waiting in line to buy tools when circumstances like this happen.
Think of it this way. If you can get SO interested in coming to get them, who do you think is going to come get them. They will just call one of their franchise dealers. They will set a value on them at some point, as they pick them up.
That dealer may buy them, or they might end up at a managers place to be sold to many different dealers.
You are not the first to find yourself in this situation. Right now you are a high risk for SO. You owe on tools and are not working in the profession any more. You say you are in good standing with them, but that could change. To repo them is much easier if you are working with the tools in an open shop. Right now they would have to track you down, and you may not even have easy access to them, even if they did find you.
Just remember, most likely a franchise dealer will act on behalf of SO in tis situation. If you worked very long at all you or someone you worked with knows how to get hold of one. Talk to them.
In the end, I would bet if you got them turned back in, and the value was close, SO would wash their hands of it. They may not even report it to a credit agency. Hell I am not even sure if you never made another payment, they would.
I would get some numbers together. The set number, the box model, take some pictures and get hold of a dealer. This is all new to you, but not for them.