Then they don’t vote, pure and simple.
*************
That is a method for sure. But you seem to be okay with
disenfranchising a voter because of not being in their
locale on election day because of some legitimate reason.
There should be a legitimate and legal method to allow
these people a method to vote.
VOTE
That's it. Other than those who work for an emergency service such as police, fire, medical or something similar, everyone else gets a paid day off to do their civil duty. And those who work an emergency service can have arrangements made to ensure they get to exercise their constitutional duty as well. Or even have a polling unit set up in their place of business.
There's absolutely no reason why the system we have now should exist.