Kerry hasn't even resigned his Senate seat. There's no reason he'll quit the campaign, short of a landslide defeat, and even then he may wait a few days.
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Nah !! He will just rip a page out of the AlGore playbook and send in the lawyers. Gonna be the second time in history that the SCOTUS will elect a President.
Al Gore only tried the lawyers trick in Florida because the voting was so close, he was legally allowed a recount--and from there, he just kept suing to get targeted recounts to try to fraud out a victory. He didn't sue in the other three states which had evidence of voting fraud, nor did he sue in Tennessee, his home state, which he lost decisively in (the favorite son effect didn't quite take hold.) In the likely scenario, Bush winning by "good enough" margins, Kerry would have no case to present to the court.
As for SCOTUS electing a president... no, that's not how it went. SCOTUS prevented SCOFL from selecting a president merely by saying that state law governs elections, and Gore had already exhausted his legal recount.