It will be whatever you set it to. Generally when you select a fingerprint to you it requires a back up method which would be the pin.
You would have selected this. Hopefully you can remember what you set it to!
Probably not. Always figure I can buy another phone if I really wreck my current one. Even if it's not another 'flagship' I can buy something to get me through...
I also generally have 3 or 4 different phones on hand as well.