caciara, I should have added the 'ATC is different, you don't understand' line to the things that don't do us any favours.
You appear to want other people to give you a number - a number of staff on duty - without any other contextual information to support your view that single-man operations are a bad thing. I am offering the view that it's not as simple as that and that every situation needs to be considered on its own merits.
I am quite aware of the material that Eurocontrol produces. Some of it is good, some less so. Some of it is valid in today's environment, some so out of date as to be misleading. In the main it's guidance - information about things that need to be considered, and it rarely gives black and white decisions about topics. As I recall it, there is some good stuff in the document that you mention but it's a while since I looked closely at that particular book but - like all guidance - it needs to be used wisely.
To answer your question - is ot better for an ANSP to close the ATC service during night hours than to keep it open with a single ATCO - it depends. You started the thread by citing a hub operation as your example but now it's any airport. The situation is very different for services at hubbing airports than for those where the same traffic is spread out over a longer period. So you have to look at each situation and make sensible assessment of what resources are needed.
I'm not one for crying wolf or citing extreme examples to support my case but think back to Ueberlingen - how many staff were on duty, two? Or was it three? And that didn't have a very good outcome.....