How long will an offline ID stay valid?

Hello

I've just got a small question because it happened a few times now.

How long will an offline device keep its ID?

We have a few devices which are offline for longer periods of time and every know and then the ID changes, so I have to get in contact with the people on site to tell me the new ID.

It would be good to know how long an ID stays valid. We might be able to plan accordingly so the devices won't lose their IDs.

And because it is more or less related, a second question. Will a device lose its ID if hardware is changed? Similar to when Windows tells me that it needs to be activated again?

Cheers!