Do I need to replace this sub floor after bad tub installation?
Yes, it appears that you need a need new sub-flooring. Once the old tub is removed clear out all the old rotted material down to solid wood.  If necessary let the area  dry for a day or so.  Then as necessary fill voids and holes with shims and filler strips. Overlay the entire area with new quality heavy sub-flooring. Then set the new tub.