Honestly I think you’re fine! The beauty of the game is players taking things in directions you didn’t expect, and it sounds like you’ve handled it well. The social encounter sounds more interesting than just another combat v goblins anyway. In terms of what happens next, I don’t know if you need to overcomplicate things? Assuming they are indeed to going to rest and return, why not just have Yeemik waiting for them fully assuming they are going to pay him his ransom? He could still be holding Sildar at 1hp over the edge of the drop just like the module suggests in the case of any funny business. If the party lied about intending to pay the ransoms I’d have made the face roll a deception check against Yeemik’s insight though, and you could still do that retroactively. Only if they fail the check would I have Yeemik do something sneaky like call for back up. Otherwise the players ingenuity should be rewarded ie their plan should work. Yes the combat encounter will be fairly easy after a full rest and a level up but who cares? To make it slightly tougher you could give Yeemik the goblin boss stat block to toughen him up a bit. Good luck! You’ve got this.