What steps should I take if I leave Thailand on a Non-O retirement visa for four years?

Do you mean 4 months?

Get a re entry permit and return before your extension expires when you return you need to file a new TM30

If returning before expiry:

Reentry permit from immigration office or airport if required.

File tm30 on return at immigration if your office requires it.

If you are away for 4 years then you start back at zero and the requirements in 4 years time will probably have changed

I doubt you have a Non-O retirement visa and instead I would almost bet if you looked at your passport the stamp says "Extension of Stay Permitted Until" and has a date, and you get that stamp a year at a time at the immigration office.

IF that is the case what you do is you go to the immigration office and buy a re-entry permit for 1000baht <- that will let you exit/re-enter the country one time and get stamped back in until the stamp you have now expires.

Notice I said you get stamped in until your current stamp expires when you return to thailand on a re-entry permit

What that means is IF you're going to be out of the country when that stamp expires you lose everything and have to start all over from zero, first with the Non-O visa and then the year extension

you get a re-entry permit at the immigration office where you got your yearly extension and where you do your 90 day reporting OR at the airport on the day you fly out