Contract?
Does it say anything in his contract? It's highly likely that there is something in it that refers to the HSE requiring flexibility to meet the needs of the service, or something like that.
I'm working in a similar area. Even though I work regular hours, in a convenient location, my contract would allow my employer to make changes if the service required it. So they would be covered if they suddenly required me to move location, or work evenings and weekends.
Since Croke Park and Haddington Road - we have increased hours, and increased flexibility is also expected.
To be honest, it sounds like your husbands boss was great to be able to accommodate him working closer to home for a while, but I wouldn't assume that it's an ongoing entitlement.