I just created a recipe for when my core goes offline, and I then had to create another for when it goes online.
It would be nice if there was tree selections, online/offline/changed, or something like that.
In the recipe there is already {{Status}} to set the status it just entered, so it would make sense to just have it check if status changes too. (I got something similar for when my phone enter and exit a location, it is done in the same recipe)