However, after all is reestablished, the normal life resumes and Bitcoin actors want to relaunch the Bitcoin network.. So first: not everybody have the same copy of the blockchain as some nodes continued recording after the others got interrupted ! And what if some entities wanted to fool the word creating completely artificial blocks and adding them to the blockchain ? How to trust a copy of the blockchain then ? Do all late copies should not-trusted/canceled ??
It would be too expensive to maintain and implement because of difficulty adjustment
Especially if the black out doesn't last long.
And even if they are able to bypass the difficulty adjustment
Once everything is back online
Offline nodes would sync to the last honest blocks
And as more comes the POW gets higher than the fake block mined.
Most POW wins not first come first served.
Such shutdown will never be possible,
That's what the dinosaurs said
The thing is anything can happen. There are lots of things in the universe we still don't know.