My father is a field-service engineer for HP in Midwest (based out of Minneapolis, but he has calls all over from Fargo, ND to Mpls, MN to Madison, WI). He is _the_ go-to for their biggest, most senior, most mission-critical clients. He put together UMN's Alpha setup, is the only guy that USPS will call for help, MNSCU, Best Buy, UHG... basically, anyone with an HP setup (server or printer) that's a Fortune 1000 (and…
If there's as much demand for him as you're describing, he could probably make a much better living doing consulting for these companies than he could working for HP.
In his shoes, I'd also make sure I keep contact information for all his best customers. Because if he gets laid off suddenly, he'll want to go back to them at least to say, "Hey, do any of your vendors need a reliable field service engineer?"