The fumigant used for drywood termites is a very thin gas. It is supposed to penetrate deeply and be all gone before anyone considers re-entry. Perhaps some gas might remain for a while in things like the sponge-rubber of furniture but it will dissipate fairly quickly. I wouldn’t worry about washing utensils but I’d probably go through his pantry and dump some food that worried me.

It is much easier to go in before the application and double-bag (Ziplocs or similar) anything that might be a concern.

Bottom line is to ask the company that did the work. Make sure they have allocated the right venting period and have properly cleared the house. If the job has been done according to the rules, he probably can move back in with no worries. To be super-safe, keep him out for another day or two.