If the college lists specific grade or GPA thresholds, then you have your answer for that college.
If the college vaguely says something like they expect you to maintain your academic performance, then you basically have to guess what will trigger a rescission. Generally, a D or F grade, or a schedule change that they do not see until the final high school transcript, is a high risk. If none of these apply, and your GPA is equal to or higher than before, then you should be safe. If your GPA is lower, it depends on how much lower, and you do not really know how much lower will trigger a rescission. Going from a 3.8 to 3.7 is unlikely to trigger a rescission. Going from a 3.8 to a 2.8 is higher risk. Going from a 3.8 to a 2.1 is even higher risk.