Consequences for foreign students of being dropped from a class?
My wife, who has some experience in these matters, says the following:


If the student is dropped from the class, making them no longer a full-time student, then they may lose visa status and be required to leave the country within days.
If the student fails, however, then it is up to the college whether to kick them out or not: so far as immigration is concerned, what matters is whether they are a full-time student, not how well they are doing.


Another possible option, which may or may not be possible in your institution, would be to try to arrange a late transfer into another "class" like an independent study, which would have no transcript value but would preserve full-time status.