With the cover back on (which I assume is how the old tenant left it) I very much doubt that a prospective new tenant would notice - but they probably would notice the absence of electricity
I certainly wasn't suggesting that, and I'm not sure I understand your point. There is only one meter connected to that fuse, so I doubt that there are 'other users' (other than the tenant of the unit).
Yes, maybe - but there are all sorts of possibilities. Indeed, if it had been there for some time, it's possible that he/she had just forgotten about the link - or, of course, that link may (behind a closed lid) even have pre-dated the recent tennant's tenancy!