Is it possible to keep phone plugged in a powerbank when the battery is worn out? Is it possible to glue a powerbank to the back of a phone, and keep it plugged in permanently, if the battery has been worn out?
My experience is that the answer is yes.
For some devices, I have completely removed the battery and have them running just from the charger.
Of course, if there is a power outage, the device will immediately turn off without saving anything.  So be aware of that possibility.