It had many defects which contributed to the disaster; from the inadequacy of its seawall, to the location of its emergency power switch-gear, to the vulnerability of its seawater pumps. Every single one of these things contributed to the disaster, and you'd have had to fix all of them for it to not have occurred. I highly doubt they would have accomplished all of that in one go.

EDIT: And they were already at least 11 years behind on that work at that point.