The "independent" corporation that owns each rig and somehow magically has no affiliation at all with the petroleum company that takes the rig's output will say "whoops, we have no money to decommission the rig and no assets to seize to pay for it, bye suckers!" and promptly go bankrupt and leave governments holding the bag.
How very dare you suggest such a thing. This kind of thinking must come from your warped mind, and very definitely not be based on the slew of mines and chemical plants left to poison the landscape, and especially not the multitude of poorly-capped methane-leaking oil wells scattered around the US by those same companies!
Knowing humans: build additional ones, but also keep these ones working past their eol date, after all, the short-term financial side effects of destroying all the things are negligible, and the profits huuuge.
Am I insane for thinking one of these would be a cool place to take a holiday? I need a time out from society and being in middle of nowhere on the ocean would be otherworldly.