The 28-year-old, who is competing on TV show Strictly Come Dancing, trained with Saracens ahead of the move.
And Williams, a team-mate of Henson's at both club and country, believes his international return will follow quick on the heels of his domestic comeback.
"I'm sure he will play for Wales again," said Williams. "We all know what kind of talent he is. He's certainly an individual who will keep himself fit. He certainly won't let himself go.
"I watched him on Strictly the other day and he's probably in the best nick he's ever been to be fair.
"He's one of these players that as soon as he's had a few games he will start playing some good rugby again.
"I would love to see Gav play for Wales, whether it's this year, next year or whenever.
"I would certainly prefer to see him on the field rather than on the dance-floor."