They will stomp through Day 1 and 2. Onoki could probably take out Konan, Hidan and possibly Sasori but would ultimately fall before the overwhelming numbers and Pein, Kakazu and Kisame. Day 2 would be a stomp without too many losses imo with Kizame taking down the Mizukage. If somehow she did beat Kisame, she would lose to Pein or Kakazu.
They'd lose on Day 3. Given the losses they've already attained they're forces are pretty depleted. They've probably got about 7000-8000 Zetsu and only Pein, Kakazu and Kisame left (Provided he beat the Mizukage.) Kisame will lose to the Raikage and Killer Bee. Gaara will provide a real match for Kakazu but with Kakazu gaining the upper hand the rest of the Sand Village will have to help him out. Everyone else faces Pein and when Raikage, Killer Bee and Gaara are done they will help them get the win. Pein is defintely the real threat here but I think he would fall eventually. Zetsu army would get overrun by Shinobi army who probbaly contains quite a few powerful jonin level ninja (Zetsu seems about Chounin level to me).