He never said he wouldn't play, just that he's taking it day by day. And he said he definitely wanted to play at the Olympics some day, so he hasn't even said he's definitely playing 2020 either.
""Day by day, honestly, I'm getting ready for the [NBA] season - and then whatever happens, happens," Simmons said.
“I definitely want to represent Australia in the Olympics, in the future.”"
Sounds to me like he is being conservative, but if he is healthy, and if the Kardashian ass plague doesn't consume him, I would be surprised if he didn't play.
Also, if I were Lemanis, I'd be offering for him to play restricted minutes for the pool games and warm ups. To be fair, no Australian is going to be playing more NBA minutes or working harder next season than Ben Simmons, and they should try to facilitate him in all the ways they can.