The best course of action for Israel is to invade and go back to their old First Intifada policy: anyone caught doing anything to impede the IDF gets their arms broken with rocks. They shouldn't reclaim Gaza, they need to focus on the hostage. Afterwords they need to tell Hamas that they have one more chance and if rocket attacks on Sderot and other cities launched from Gaza don't stop and if they won't get their act together, there will be hell to pay. Israel left Gaza; you think these psychopaths would appreciate it instead of trying to coerce the Israelis into coming back.
The israeli's launched some rockets on a Gaza beach before Hamas responded. It was the israeli's that coerced the Palestinians, not the other way around.