USA - Undergraduate Final Transcripts and PhD Programs
There are no "laws" that describe what schools can do in such situations. Everything depends on how strictly the department obeys whatever regulations are in place. Some may say it only counts when the decision is made, and others will insist on it being valid at the time of degree completion. Many schools do not have strict GPA cutoffs for admission, in which case the issue is moot.

In general, though, I don't think I've heard of a school withdrawing an offer because of a small change in GPA. Usually it's when someone contracts "terminal senioritis" and has their GPA fall drastically after the admission offer is made.