A friend of mine is leaving Thailand after his contract is up and his non B expires at the end of March. He wants to travel a bit before heading home. I know it's up to the immigration officer but would one anticipate any issues doing a visa run by air and coming back in on a visa exempt entry so long as he has a flight out?

No problem for him to get a 30 day visa exempt entry since he apparently may not have done many of them recently.

Not sure what he has since you only wrote about a non-b. I suspect he actually has a extension of stay issued by immigration that should be canceled before he leaves the country.