if spotted leaf didn't die would her and firestar be mates even though it is against the warrior code?

probably

i hve no idea

No because FirexSand makes Squirrelflight and Leafpool and Squirrelflight would have needed to be alive for the огонь and tiger prophecy, and CrowxLeaf makes Lionblaze, Hollyleaf and Jayfeather, and those three needed to be alive for the Power Of Three phrophecy.

It would be awesome and they could still have Squirrelflight and Leafpool.