well, first off, i unloaded a bunch of gold jewelry. you dont get that much in comparison to what you paid, actually, the quality of the piece has no bearing, only its weight.
the ring cost $900, but even when purchasing, they are so overpriced. they will take out the emerald, but the stones they use in class rings arent the best cuts. even so, gemstones, besides diamonds, dont get much value. even diamonds though arent what you think. my sister has been divorced twice, and sold the rings. she took them several places. they were both quite nice rings, with decent quality diamonds. i think she ended up with 15% of the cost of the ring, if that, and that was for diamonds, which hold up value better than gemstones.
as for the ring itself, they are going to rip the emerald out, weigh the gold, and give you the going $ per ounce of the gold. it wont be much at all. they will actually put all the same karat gold together and weigh it with no regards to the jewelry itself.
its actually quite sad. the only person who will find value in that ring is him and his family. if it werent such a personal item, i would say no problem. but considering how little you will get, and how he may like to show his children someday, i would give it back. its not that hard, if you know where his parents are, just mail it to them. otherwise, put out on your facebook that you are looking for him, someone always knows someone. there are ways if you really spend time on the computer to find someone. most people are listed in the phonebook to some degree, and if he isnt, most likely his parents or siblings are. if you try a bunch of those white page listings, you usually can find relatives fairly easy.
otherwise, get rid of all your other unwanted or out of style jewelry. its not worth it unless you go with a few things, as one pair of earrings may only get you $10.