Yikes–good thing to check for folks while I believe it may still be open season. We are fortunate that our family plan asked no Qs about where anyone physically was and how much time they were out of state (some years S was only home for winter holidays and a few weeks in the summer.
The insurance plan we got for S his SR year thru his U covered him thru Aug after his graduation and we had to buy him an individual policy for Aug–12/31, when he again qualified to be in our family plan as under age 26. Check the policy carefully–we wanted to be sure there were no gaps in coverage.
Since our plan is a group plan, it still has all BCBS nationwide in network.