What with nuki of deseaded person

I have a customer with her parent. I installed a Nuki lock 2.0 at the parents door, together with a nuki keypad and nuki FOB. The parent now is demented and cannot remember the password, and we want to control the lock, but is is protected with that password. So, will the lock be unusable in the future, or can I bring it back to the refurbished state?

You can always reset Nuki Locks to factory defaults if you have physical access to the device. Just choose reset to factory defaults via the apps menu > help section.

And, as I said in my first question, if we do not have fysical access to the configuration of the app? (password protected)

Just download the Nuki App on your phone and reset it with your phone.
Your App does not need to be authorized in order to do a factory reset (if you have physical access to the Smart Lock).