I expect nothing. In theory, northern Israelis would evacuate, just like how southern Lebanese evacuates when Israel issues a warning. Of course the main difference is that Israel seldom issues evacuation warnings. Iran has been shouting "death to Israel" for 50 years.

Why would EU be expected to take military actions in Israel, Iran or Lebanon? Or Saudi Arabia, UAE, Venezuela, Cuba or USA?

Stop Israel attacking Hezbollah? Just wait. soon they will join US to help open the strait.

One of the advantages of the veto power of every member of EU is that the bloc is unable to turn into a new global (or even regional) policeman, however strongly a simple majority feels about Israel, Iran or anything else.

It would be unlikely anyway - European voters prefer butter to guns, sometimes a bit too much - but this makes the probability zero and I am happy for that. This continent is dotted with mass graves from a thousand previous wars, stretching to at least the Late Stone Age. Constant wars were one of our curses, and our ancestors launched way too many crusades for various holy causes.