In comparison - A foreigner here in Thailand doesn't renew his extension, stops the 90 day reports and is officially overstaying. What happens? A big nothing. Now to me it seems easily doable for the authorities to have a list of overstayers and pursue said overstayer. Do they? A big no.
But, the tax people are so organized they will track down a retiree and tax them, not only on the money they bring into country but money made in their home country. Now, I'm sure there are some huge money foreigners who do business in Thailand who probably should do some damage control but for the masses of retirees here I wouldn't sweat it.