I want to store a battery powered device long term (decades) as a reference article, it will never be switched on or charged again. The problem is that it contains a small LiPo battery that will be very hard to remove.
Is there likely to be any significant risk I need to worry about? Once depleted will the battery be relatively inert?
First off: I am NOT an electrician. From what I know modern LiPos are much less likely to suffer catastrophic failure. These will lose charge over time, especially if plugged into something. Unless there is a voltmeter to ensure operation only with charged lipos, however, this will be very slow. A Lipo running out in such a way might swell and definitely be damaged beyond repain. It should probably still not burst into flames. So in short: I think you should be fine.