Of course a Party can- and should- determine beforehand if someone will not be an inhabitant at such and such a date. Reasonable people, and the law, only ask evidence for a conclusion.
Kooks demand clairvoyance.
If Delay somehow managed not to ever clearly tell Benkiser that he will be an inhabitant of Virginia on the election (instead of just that he is presently an inhabitant) then he deserved to lose for such an error. But I seriously doubt that is the fact.