Question: Under what conditions would a college take back an acceptance?
Colleges do not like to renege on admission decisions but will do so on occasion. This most typically happens when a student's grades drop SIGNIFICANTLY after the student is admitted. In other words, if an A student suffers a bout of senioritis and drops to a B average, it's not a dealbreaker. But if the grades plummet to C's and D's (or worse), it can be. If there are extenuating circumstances behind this change in GPA (e.g., an illness or family crisis), they should be explained by the school counselor. The college will probably be sympathetic and stand by their original acceptance, sometimes putting the student on academic probation when the school year starts.
Colleges may also revoke acceptances if the student is suspended from school or arrested outside of school. Again, because the college does NOT want to do this, the case will be carefully evaluated and the verdict will most likely depend on the nature of the infraction and the circumstances surrounding it.
Finally, if a college should discover that an applicant was dishonest on his or her application, that is likely to lead to a rescinded admission, too.
Best wishes. I hope all your admission news is good.