Can we leave Thailand with our Non-Imm O-A multiple entry visa and return before expiration?

Just done it and all good 😎

To make it clear. On the visa itself is a Valid Until or Enter Before date. As long as you enter Thailand before this date you get 1 year of stay stamped in your passport. To get another year you have to leave and re-enter Thailand just before or even on this Valid Until or Enter Before date. After this date mentioned on the visa, the visa becomes invalid but you can stay inside Thailand till the last day mentioned in that square stamp as Admitted to Stay ../../.. . If you like to travel abroad after this date on your visa and keep your stay alive you get or a Single Re-Entry Permit for 1.000 Thb or if you like to travel more a Multiple Re-entry Permit for 3.800 Thb. On return you fill in on the arrival card the re-entry permit number as visa number and you will get the same Admitted to Stay date stamped in your passport.

Remember that in the second year you will need to purchase a reentry permit if you leave Thailand and return. Its included in the first year.

If your visa is still valid, then no problem

Yes you are. No problem.