Recovering internal storage externally

I am trying to repair a computer which would not boot after being updated. Taking it to the apple store, we were told they would need to wipe the drive in their process of troubleshooting and attempting to fix the computer. Currently I am trying to backup the data externally, however, I know the storage is not upgradeable or removable. Is it possible to do what I’m suggesting or should I bite the bullet and wipe the data? (fortunately the device is still under warranty)