What do you do when you beat zongazang for the last time.?

After you've beaten the game, tournaments will open up on all three islands, starting with Ribular. Be aware that all the tournaments will have specific requirements for your teams, so you may have to spend some time leveling up specific dinos to meet those requirements. All the enemy teams in these tournaments are level 20's and most have tricky side effects, so be prepared! When you've done the Ilium one, a Champions tournament will open on the BB Brigade base island with Stella, Terry, Kent and Joe.
The news guy in the shops on all three islands will have side missions. Complete all those.
Collect all the vivosaurs. Not an easy task, as any that the official website says are from the Seafloor Caverns get spread out over the rest of the digs sites post-game; no one has been able to figure out how to get back there yet. If you have the original game, and access to a second DS, it's easiest to get #'s 1-100 from the original FF game and send them over to the new game via the fossil cannon. This has the advantage of getting you all four bones for each vivosaur rather than just the heads and trying to rank up your vivosaur from lvl 1 or 2.
Hope this gives you some ideas. Have fun!

You can also battle robinson to get tonzilla and the bb brigade captains and also if you have wifi get dynal duna dinomaton and raptin note you have to beat them first you along with that you can get igno and frigi with wifi too! Also with wifi after you show ryne menchi after you beat the game,ryne will challenge you to a battle with a salada after you beat her you will get salada todd,rupert,and paulqueen will also challenge you to battles

Todd also challenges you (he is so easy) where do you find the leaders after the game is over. You can rebattle zongazonga and get all of the zombie vivosaurs. To the boneysaurs you battle lester, lola, and cole again.