After a reboot, macOS Sierra stopped loading and is not reinstalled - what should I do?

Question

macOS

So it goes.

I've been waiting for an hour for macOS to be reinstalled, I guess never.
It all started with the fact that the poppy gave me a message that the disk was almost completely full and something had to be done.
First of all, I closed all programs and rebooted it, but the reboot was unsuccessful - the progressbar did not even reach the middle, as the boot apple went out, the touchbar went out, only the button backlight worked.
Analysis of the hard drive in Disk Utility did not reveal any problems.
Backups, unfortunately, three months ago, there are few important files, but I need to save one folder.
Now I'm writing from a girl's macbook - I read that they can be connected using a thunderbolt wire, but it costs 5k, can I try via USB (I have to buy it, that's why I'm asking)?
What in general could happen that the hard one is in order, but nothing can be done with it?

Answer 1

O!!! Nevertheless, you need to wait, I also had this, I left it for the night. Everything will be fine - wait!
Well, you can upload the system to a USB flash drive from another poppy and reinstall it.