IIRC, BL 1 didn't have any replayable raid bosses until the DLCs came out, so there isn't a precident on how they'd handle it.
When Crawmerax came out, he was level 64 (since the level cap was 61). Then when they raised the level cap pre-Claptrap, they raised his level respectively, up to 72. So it can be assumed they'll do the same with the other bosses.
Your body may be gone, I'm gonna carry you in in my head and in my heart, in my soul.