Ok since I,m one of those glass half full kinda guys .Im thinking the op might could have done what he needed to do under deck before things went south .. Instead of jumping in and tearing everything apart he could have maybe installed some sort of temp bracing inside the hull to stabilize it . Then demo small sections and reglass new stringers in allowing for a lap joint each time . Like maybe a 4 or 6 foot section at a time .. But tearing it out at one time was destined for failure...