Yeah, VU leaving would absolutely kill UD FB. Afterall, we depend so heavily on the revenue of VU fans filling our stadium once every two years. Oh, wait, that's what we do on the Main Line.
UD FB has withstood the loss of our chief historic rivals, Temple, Lehigh and (once before) Villanova. We'll do quite fine should VU repeat Temple's mistake. They can have at it.
As for HU, URI and NU leaving, that will have far more of a financial impact on UMaine than UD, especially with ODU and GSU coming on. The net effect on UD is the elimination of one additional flight from our schedule. UMaine will be adding a flight each year. UD's in a great position, being located in the direct center of the conference footprint.
JMU isn't going anywhere into the foreseeable future, nor apparently is ODU or UD. However, all appear to be making and planning significant upgrades to their stadiums. Those who aren't considering similar investments will probably have to look elsewhere in the not too distant future.