This has apparently changed. I reactivated an account yesterday on the 90th day. It had not yet entered any decay state. Today I logged in and it is slightly worn, which didn't totally surprise me because I knew it was due, and I know it takes 24 hours to work its way through the system. I didn't think to note the exact time I reactivated, but I would guess that it's been just shy of 24 hours.
According to the in-game help (codex), it says the house owner merely needs to log in and open the door. I knew this was outdated, but I did it anyway just to say I did. Not surprisingly, it didn't work.
Eventually I paged a GM. The GM was very nice but said that once the house enters a decay state, it will fall no matter what, even if the account is reactivated. He/she offered me a refresh as a one-time exception (so y'all don't go looking for my idoc, lol!)
As an update: While I'm still grateful to the GM for being sympathetic and helping me out, it turns out that asking for his/her help may have been unnecessary; the policy hasn't changed, and the GM was mistaken on the information. Sometimes it just takes a little more than the usual 24 hours, and I panicked. I guess that's what I get for trying to cut it so close!
