Do abandoned buildings sort themselves out eventually if you just leave them?

Solution 1:

If there is a need for the zone type, yes, abandoned buildings will eventually sort themselves out. If, for example, a high-density residential building becomes abandoned, the lot is free for new high-density residential development. However buildings that replace an abandoned one will start fresh at base level and need to work its way back up over time. Effectively no different than had you bulldozed it.

There is a downside to leaving them to sort themselves out - an abandoned building reduces the happiness values around it, has increased crime rate, and is a higher fire hazard. All of which can conspire to reduce the property values of the land they occupy and the surrounding area. This makes the land less desirable to develop, and can potentially cause surrounding areas to themselves become abandoned.

So it is typically the superior choice to manually bulldoze abandoned buildings than letting them sort out their own problems. If you are not terribly concerned about achievements, there are mods available on the Steam Workshop that will automatically bulldoze buildings that become abandoned or burn down. This can be a significant time saver when your city gets sufficiently large.

Solution 2:

No, demolishing them is not necessary because eventually they will sort themselves out. From The game manual:

If the abandoned buildings are not bulldozed, they will be inhabited again after a minimum of 4 weeks of in-game time. Burned down buildings need to be bulldozed to make room for a new building.

So you don't have to demolish abandoned buidlings, but demolishing has the following benefits:

1. Avoiding 4-weeks wait.
2. Improving the land value around that location.

And you have to demolish burned down buildings, though, they will never recover on their own.

Solution 3:

It's possible for a building to stop being abandoned on its own, if you have very high demand for that zone type. It will go through the construction animation again and then be back at the base level.

However, if you have a lot of abandoned buildings, the negative impacts of having abandoned buildings nearby can prevent this from happening. This is why bulldozing is generally a better solution.