unsummon on damaged buildings?

How does damage work on unsummoned buildings in relation to resoucres gained?

Eg. if a building has 50% hp left, will you only regain 25% of the original resources?

Unsummoning your building will give you 50% of the spent resources. But this only works if the building is at 100% hp at the start and doen't get any damage during the process. Any damage taken before the unsummoning or during will decrease ur resources gained with the following formula:

RessourcesGained = (BuildingCurrentHP / BuildingMaxHP) * (50 / 100) * BuildingResourcesCost

This means that if you play against undead and get hold of an unprotected expand and he starts unsummoning, you usually want't to do as much damage as possible to the building which has the best ratio of beeing fast to kill to the price in resources. You will deny your enemy some valuable ressources with that.

The building will get fixed % damage per second. This means that a Necropolis will unsummon as fast as a Tomb Of Relics or a Ziggurat. The armor of the building is not affected and the attacker will not get any additional buff to his attack against that building.

Last thing is that you can't stop the process once you decided to unsummon.