Recovering files from an unbootable partition in OSX I have a MacBook previously bootcamped to Windows 10. The internal hard drive had 3 partitions:

200MB Partition 0
249GB Partition 1 (OSX)
250GB Partition 2 (Windows 10)

The model is a MacBook Pro mid-2012, and Partition 1 has OSX 10.15 Catalina.
I've made a fatal mistake of accidentally deleting the 200 MB partition via the Windows 10 install disk. I wanted to reinstall Windows 10 to fix some audio errors. Now I'm trying to recover all the files I have in the OSX partition. Before I made this mistake, I've backed up all Windows files on the OSX partition.
If I go to disk utility via Internet Recovery on my Mac, the list of disks and volumes has a &quot;disk0s1&quot; volume that I can't verify nor repair but can only be partitioned away. If I ever re-partition or reformat that hard drive, all data will be lost. I need to recover the files before I do anything.
diskutil list prints out:
/dev/disk0
#:                   TYPE NAME SIZE      IDENTIFIER
0: FDisk_partition_scheme      *500.1 GB disk0
1:                   0xFF      249.0 GB  disk0s1

gpt -r show /dev/disk0 prints out:
    start      size index contents
        0         1       MBR
        1         1       Pri GPT header
        2        32       Pri GPT table
       34         6       
       40    409600     1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
   409640 486328128     1 MBR part 255
486737768       152       
486737920 490035200     3 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
976773120        15       
976773135        32       Sec GPT Table
976773167         1       Sec GPT header

The tools I currently have for this situation:

Windows 10 installation USB
A Seagate External portable 1TB hard drive
I will post this as an answer although there are some uncertainties since some info is missing.

A 200mb Partition usually is the EFI partition (more detail what this is) which allows your Mac to boot into Windows.

Deleting this does not at a all delete your actual Mac/Windows partition. Therefore, I doubt you have actual done too much harm.
It is not clear if you have tried and failed, but you should be able to boot into macOS. After startup go into the finder and show all drives (finder hit cmd, select sidebar and tick everything that says disk).
You should then be able to see the remaining two partitions, Macintosh HD and some other name (e.g. Windows). Usually, you can simply open either and then do whatever you want, e.g. clone one disk, save the data,...