I'm sorry to hear some of your DC are struggling. But I'm not surprised - it's a big transition and disconnect from all your usual comforts and customs. It's perfectly natural to take time to find your feet and your people. I remember this happening to a number of my friends back in the day.
Even then, I'm sure those whose DC have dived straight in are very aware that it wont all be plain sailing from here. There are bound to be bumps in the road and fallings out. You might hit it off at first, but hard partying might just delay the recognition that you don't have as much in common with your first friends as you thought.
DD and I talked about this a lot before she went (she had an extra year at home doing an Art foundation course before going). We recognised how high the expectations are to have an amazing time and meet millions of friends. We discussed the fact that first friends are not necessarily your forever friends and that group dynamics can shift and fractures occur down the track. And knowing my DD there is always potential for disappointments and dramas with her friends! I won't be surprised at all if she's in the phone about this in a few weeks time.
All we can do is be there to listen, encourage and try to instil hope. To recognise that making friends and growing a sense of belonging and fitting in isn't always easy and can shake the confidence. And to reassure that things can and often do change.
I know a few people whose DCs have not enjoyed their 1st term. Some soldiered on, others started again a year later. Older and wiser. And yes - with an extra year of loan. But I don't know anyone whose kid has dropped out and not moved onto a new college. So their will wasn't broken by the experience. It's a very random process - who you live with and who you meet - it's bound not to be right every time.