Has Bethesda ever made clear what happened to the ruins of the Oblivion gates in the time leading up to the return of Alduin 300 years later? Reason I ask is that the developer of Oblivion's Open Cities mod has brought his magic to Skyrim as well, bringing back the open feel that Morrowind had, but with the side effect of having included empty Oblivion gates as well. I understand that the crisis did envelope all of Tamriel and not just Cyrodiil, but is it really plausible that after three centuries the populace would not have cleaned up the ruins? I would've figured that Bethesda's omission of them in the first place would have been enough to indicate that yes, the people of Tamriel did, over time, clear the rubble of the gates away.

I was relieved to find another tiny mod that removed the gates that were added with Open Cities. I"m just curious what the "official" lore is on this point.

The gates dissapear once they close. Aside from scorched ground and a handful of non-native flora, there's no evidence of them ever being there.

That's what happens in Vanilla Oblivion. It sounds like Open Cities adds some permanent gates.

Infernal City tells us that the physical gates remain even after they've been closed. There's a town built around one of the ruined frames in Cyrodiil.