I mean do they need to be worth anything for them? If it works it works. There is value in it only if selling - else if they are using it for the foreseeable future then the only value it would have under normal circumstances is it's junk value.
The real issue is that they’ll be forever restricted to Russian airspace.
That's no problem for Aeroflot. Just like it's no problem for me that I can't take my Mercedes out of the country either. Not that I would ever need to do that, anyway.