Next time, they will call it a "very serious breach" of the cease-fire, and urge Israel to exercise maximum restraint. The time after that, they can escalate to "extremely serious breach."
Begin war of the cities. Israel knows where the Hezbollah families and villages are. If Israeli settlements are targetted, those villages will be targetted. If the Lebanese Shiites want to take sides, their villages are also targetted. Isreali settlements have good bomb shelters, the Hezbollah have none for their civilians. How can you fight a war where your enemy attacks and kills your civilians and you respond by looking for only the attackers?