TM30 has always been required for tourists, even long before people or House Owners had to do it themselves. Any tourist that stays in a hotel has a TM30 lodged. It is just that if you don't need to extend a 60 day visa exemption and visit an office, you will never be asked for it.
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.