Happens all the time at my school. Local leave for the state MD school when the get The Call.
If this happen during orientation week, we have a panel of alternates, who serve the same function as those on a jury. If someone leaves, they get a seat. If not, they enter in the next year's class.
I don't know if MD schools do this, but the COMs are allowed some attrition seats, so my school, for example, which has ~100 students, actually is allowed to matriculate, say, 107, to account for those 7-ish who decide to go elsewhere.