A guy I work with, his father in law, put out 1.5 gal of 2,4-D over his entire yard (0.5 acres). It's obviously killing the St. Augustine like crazy. Anyone have any idea if this grass will make a comeback and how long it would take or will he need to completely start over?

What was the concentration? If it was the standard 4# ai/gal amine, that's 12# ai per acre………I'm guessing the lawn is toast. At that rate, even something like 2.4-D will hang around for some time and be toxic to even new sod. Mix a gallon or two of molasses in enough water to spray the yard. Add a good layer of compost, water and wait 6 or 8 weeks before sodding or reseeding.

Was it a sunny day when he applied?

Think it was the concentrate from Lowe's or TSC whatever they got there. I'll tell the guy I work with about molasses

Not sure on that but I believe it was before some decent rains. I may be wrong though it could have been after like 1" of rains