It was a one shot that took place over two sessions and four in game days. The first was mostly what you described, but that night a goblin band that had split from a Horde on it's way to attack Yartar raided the farm. The next couple of days were our group of survivors trying to reach Yartar for safety with as many supplies as we could while dodging other goblin bands and staving off exhaustion. The boss fight I described earlier was a scout group that we had to defeat in order to reach one of the city gates and get inside the walls.

This is one of the few campaigns I've ever been in where animal handling really mattered since we had an ox that was carrying a lot of supplies we would need to survive the siege if we made it to the city.