Something they could add could be that after most of the goblins are dead from however the fight ends up going, then a couple more come up with some sort of explosives to blow up the gate. One of the companions or even our own character if playing solo could then make a comment about we had better help the defenders if we want to find that healer. This would probably be less complicated than removing all assumptions of us helping.
From a warfare perspective, you would not bring a siege equipment to a raiding party. The goal of the first goblin party is not to sack the grove but kill the survivors from the expedition and potentially acquire loot and food.
I do think helping the defenders & by extension Wyll should be optional. If you have not, I guess you can still get access to Kagha as she is in desperate need for some outsider's help to get rid of the tieflings. The same is valid for Zevlor. If you are a tiefling that might introduce you to Zevlor who can send you to Kagha. For drows, I guess this might also work as you are a predominantly non drow party.
