This is one of my most brain melting questions I have read for a while. Get an onward flight, to prevent being denied. If you were denied, then it must be for some other very serious issue like too many visits, previous overstay, not a tourist and appearing like you live and work in Thailand. So in this case, you should get a visa, instead of trying to use a visa exemption. This is now much easier with the introduction of the DTV scheme.
It would be possible to get a re-entry permit and return on the same visa. But it would be best to get a 1 year extension of stay, and a re-entry permit.
So this would be your first year on the OA? If you leave and come back in, before the visa expires, you would be stamped in for another year without having to put any money in a Thai bank account. Although, the insurance would still be required though. Or leave and come back in to get a NON O, with no insurance required. Good luck.