Iranians in the West are not representative of those in Iran. One thing they have in common (with protesters) is the removal of current regime. Not a return of a monarch who might have the same dictatorial powers of his father.
Then there is still a sizable bunch of regime supporters. So even if the regime is ousted, it doesnt mean smooth sailng ahead. It could mean civil war.
Israel knows this (the US too dumb to figure it out). Because if the regime was gone, its replacement, even if a moderate or secular govt, will not likely pander to Israeli whims or conditions. Israel in the eyes of the people of Iran is just as evil an entity as it ever was. So any future Iranian govt that comes will not likely be friendly to it. Therefore Israel and its operatives on the ground may try their hardest to stoke a civil war.
If a civil war should unfold, it will likely result in a very weakened Iran that will not be able to do much about Israels expansionist goals and adventurism in the region, including taking over all of Syria or parts of Lebanon. I think thats what Israel is banking on: for Iran to plunge into continual turmoil where its priorities are focused more inwards than out.