they have spare parts for older models for repair, they will also hold some refurb units for cases involving replacements
you won't get a discount, you can trade it in, but if it's cracked the trade-in value tanks, so it's usually your best bet to repair it before trading it in
i always get apple care because it's a no-brainer
there are tools available to make this happen, but it's usually used by spies on world leaders because it costs literally millions, look up NSO Group
so no, probably not.