Hezballah-Syria-Iran weak spot is in Syria where they need USSR help to contain rebels.
If Hezballah's forces in Syria are weakened, sunnis will be able to take revenge on shia's from Syria to Beyrout, passing by Beeka.
And maybe also by other minorities who will pass to the strongest side.
Shias are more scared by sunnis militants than by Israel, because they know that such as ex-al Nosra don't play by Geneva rules.
Shias killed Hariri, imposed their rule over sunnis, there are a lot of accounts waiting to be payed in blood.
Will Putin find some advantage in this deal? Will it weaken enough shias to make them dependable on USSR's might and turn them into political clients?