Is it part of a plan that Hezbollah will do defense once areas are won back?
I don’t think so. Since Hezbollah is essentially an overseas brigade of the Iranian Revolutionary Guard Corp (IRGC) I think they got instructions from Tehran to pull back now that Russia is in the game.
I feel certain that Putin told Rouhani, “Get your scumbags out of my area of operation.” Or something to that effect.
Defense-only is just one step above withdrawal. Sounds like their offense was very costly.