Recreate EFI partition

So, I was persuaded to do a colleague a favour (that was my first mistake...). He wanted me to clean the EFI partition of a USB stick using my macbook (his machine was borked). That wasn't something I knew much about but he had the terminal code to do it and seemed confident. But, not surprisingly, it got messed up and it looks like I deleted the EFI partition of my Macbook (Retina, 12-inch, Early 2015).

When I rebooted the machine, at first it wouldn't boot. By holding down the option key, it opened up recovery mode, asked me to enter wifi credentials and then choose a boot disk. It then loaded. So it looks like something is messed up.

I have backups. I have the official High Sierra installer sitting in my applications folder ready to go. But will reinstalling the OS be enough? I suspect that won't recreate the EFI partition.

So: how important is that partition? Assuming I need it, how do I get it back? What should I do, and in what order should I do things?

The terminal instructions we followed were:

Type: sudo -s

Enter your password

Type: newfs_hfs -v EFI /dev/disk?s1

Type: mkdir /Volumes/EFI

Type: mount_hfs /dev/disk?s1 /Volumes/EFI

Close Terminal

In the above, the 'disk?' the question mark needs to be replaced with the CORRECT number of the disk to work properly. To be honest, if you've stumbled on this posting, don't trust the above or use it at all with checking with someone who knows what they are doing.