Personally I would prefer "manned fortifications", where the workers actually fight with militia gear if the Hex is attacked. Without someone guarding it, a fortification is just waiting for the enemy to take it from you:
https://www.matrixgames.com/forums/tm.asp?m=4843059
As public assets they could be cut off from supply and then cease to function. They also would be maintained by civilian workers. I think that real fortifications are maintained by soldiers (including the men who man them) and that their benefit wouldn't suddenly disappear if for two months they didn't receive trucks or trains bringing supply.
Actually for large fortifications a large amount of civilian workers are needed to build them. Even if you got a massive engineer corpse like germany in WW2, a lot of the work is done by slave labour rather then soldiers:
https://en.wikipedia.org/wiki/Organisation_Todt
If the hex does not get supplies, then the soldiers starve same as any other cut off troop.
Minor restoration would fall under the Units building entrenchment.
I guess they would also be no Civilian workers there to do relevant repairs (actually restroing the HP of the Asset).
ORIGINAL: newageofpower
The problem is, with the way combat interacts with Assets they'd get smashed apart pretty quickly.
Well I think asset destruction (intentional and due to fire) as well as swapping out should get a pass anyway:
https://www.matrixgames.com/forums/tm.asp?m=4837855
This would be just one aspect to it.