How about if either Iran or Syria become involved?
Just for fun let's say Israel continues to bomb the shit out of Beirut and the Lebanese government collapses. Hezbollah continue to fire missiles into Israel, so Israel goes for the full blown land invasion, scorched earth policy and all. Syria complains to the UN, but the US and UK veto any moves in the Security Council. Syria announce it is sending humanitarian aid by convoy into Lebanon. Israel suspects it is a cover for military equipment and bombs it. Syrian Army sends troops to protect next convoy, IAF bombs it and kills Syrian soldiers. Syrian government send troops back into Southern Lebanon, Iran fires Shahb-4 missiles at Israel...
You can now derive whatever ending you like from this scenario.