If a battery powered sensor changes state during a power failure then ST will miss it.
1 - Contact sensor is in the closed position
2 - The power goes off
3 - Contact Sensor opens
4 - Power back on
After the above, ST will display the door as closed even though it is still open.
Closing the door with the power back on will re-sync though.
Your Aeon Labs switch will likely revert to the off position as @JDRoberts states. I can’t find any documentation on this either way so you may be better of running a test.
Some mains devices (i.e Fibaro Modules) have customisable parameters and you get to choose what happens: