Well since your friend is footing the bill, start with a complete trans fluid and filter change and make sure they drain the converter. Tell the shop what happened and ask them to look real good through the fluid and make sure there aren't any metal shavings floating around in the trans. If there are, you will probably need a new trans. Also have them pull the diff cover off and check the backlash of the diff and look at the gears to make sure nothing got screwed up in there. Probably replace the U-joints in the driveshaft just to be safe, or at least check the play in them. If you have a stock driveshaft, look at the part where the 2 halves are crimped together and make sure that doesn't look like it twisted or came apart at all. Also check the CV shaft for excessive play, and check both rear hub bearings. Last but not least, have them hook up a scan tool and go through engine, trans, and ABS systems to make sure there aren't any codes in the system. Just because you don't see a light on doesn't mean there isn't something wrong. Most likely your car will be alright, but have them check everything on this list because if they don't, and a few months from now you start getting a vibration or a noise, you don't want your friend to say that it isn't his fault and refuse to pay for it and then you'll be stuck with say a $600 bill to rebuild the differential for his stupidity, see what I mean? Good luck. Hopefully everything will be alright. If not, at least you'll have your own personal servent until he pays for what he broke.
Mike