Apartments are not the same as private chambers in a FC house. They are not subject to demolition. You can take a 2 year break and your apartment will still be there when you return to the game. You could buy the items you want, place them in your apartment and not worry about losing them.

I still wouldn't suggest spending real money on housing items, though. If you feel you must have them, keep them stored on a retainer instead of in housing storage when not displayed. That's what I do with the items I've picked up from seasonal events over the years.

As for adding them to the Calamity Salvager, I suspect they won't do that because it's far too easy for players to obtain duplicates to sell to other players. Personally I'd rather see them leave the items on the Seasonal Event vendor available for purchase with the seasonal event currency (there's usually some repeatable quest or FATE that can be done to earn it). I doubt it would ever happen though with it being a source of revenue on Mogstation.