If LSU were to withdraw (I'm not expecting this to happen), surely the brackets would be adjusted. Right?
Of course, if the withdrawal came later rather than sooner then re-seeding would be unlikely.
I would think the brackets would have to be adjusted. Rather than withdraw, the more likely scenario may be that the SEC vacates all their league wins, dropping them to the 14 seed.
If any action is taken, I would look for an announcement ASAP, probably today. Game prep and travel arrangements are on the line for everyone, so time is of the essence.