Not to discourage other answers, but you might find these previous posts to be helpful:

• What was the back up plan if d-day failed? feat. /u/KroipyBill

• Was there a "Plan B" if D Day failed? Or was it simply going "All in"? feat. /u/Rittermeister

They're both older answers, but the general consensus seems to be that no, there was no real backup plan in place. Hopefully someone can come into the comments and expand on this a bit. Hope that helps!