A Georgist LVT would fix that is short order. Start making owners pay compensation for keeping a valuable space empty and crumbling, and you'll see them step to it pretty quickly or sell it to someone who does.
If it's empty and crumbling, I doubt it's all that valuable to be repurposed for housing or anything else. I did note the other day in the very small downtown of a nearby minor city that the the ancient travel agent is now a party supply store. But, really, there's not a lot in that downtown.
The point of LVT is right there in the name: it is the land that has value. "Location, location, location" is an old cliche for a reason.
If you let your property go empty and crumble, the Land Value Tax is there to provide the incentive for you to either fix up the property and actually use it, or sell it to someone who will.
The state takes it, and then can either sell it off or use it. This makes it easier to do things than trying to find who owns a probably abandoned property.
This is essentially saying "There's no hope; no one will ever return to downtown, no matter what!"... in a thread trying to find ways to prove that wrong.
Though I am pro-LVT, I don't think this will help in the current situation.
The owner, the bank, and the city all wish to maintain the illusion that a $10M building from 2010 is still worth at least $10M today, even vacant. No party wishes to realize the loss in value. Occasionally, the city may try to punish vacancy with a tax, which is still about additional revenue and not about realizing diminished value.
Let’s assume that 10m is the land and it’s a 5% tax. That means the bank is paying 500k a year to keep an empty property. That’s real cash flow problems.