Plenty of kids crash/burn in first semester. I had two different kids flame out first semester. One pulled it together and stayed at the school and graduated on time. The other one (who was a crazy spender like your kid) got pulled from school, spent a few years working and going to CC, and finally graduated from another school on the six year plan. I think you are actually in a pretty good position to figure out what is going on and what to do about it.
For the next two months, the kid is not living in your house but is in a relatively safe place. Food, shelter, medical care, classes, books and phone are paid for. So even with absolutely zero money, the kid will not be homeless or in distress. So you need to make good use of that time to investigate, diagnose and decide.
First, put the kid on a reasonable but low cash budget, which you can fund weekly onto a debit card. No other access to cash or credit. If there’s an emergency, you can always get cash to the kid quickly. Make sure you can see the debit card transactions. Be on the lookout for cash withdrawals – for my kid that always meant drug purchases.
Second, be upfront with your kid that he (very luckily) has been awarded a full ride to college, but that the Mom/Dad full ride is renewable on a semester-by-semester basis. Make it clear that you have not yet written the check for spring semester and that you won’t be doing that until after the returns from fall semester are in. I wouldn’t get bogged down with anything specific like a GPA requirements. For now, just let the kid know that he needs to be serious and responsible about school and that, if he’s not, his full ride can easily be put on hold until some time in the future when he’s more pulled together.
Third, make your kid turn over all his passwords for the university email and online academic systems as a condition of the full ride. You don’t have to look at those, but your kid needs to know that you can. If he’s having problems (academic or otherwise) it will show up there. If he knows you can see that stuff, he’ll be much more forthcoming and honest about what is really going on. It is just so much easier to log onto the kid’s accounts directly yourself than deal with all the university privacy BS. Since the kids communicate with friends mostly via social media, you are really not intruding too much into the personal by accessing the university systems directly.
Fourth, after laying out the parameters above, listen to your kid about what is going on. Could be anything – a bad college fit, mental health, drugs, booze, etc. etc. Do this face-to-face asap.
Good luck.