My most recent game of Fantasy saw us roll the Watchtower scenario. Now, Skaven have two ways to destroy buildings and I was equipped with both. On the first turn I rocked the building with Crack's Call, destroying it. The rulebook fails to provide an answer for what happens if it is destroyed, we assumed that it still counts as the main objective. However, since it's now a ruin you can have multiple units in it, so it's not as simple to determine the victor.
To resolve this we decided that if one side had the ruin with no enemy units touching it, it would be a win. If there were an enemy unit "contesting" the objective (touching it) we would go to the secondary victory conditions provided in the rulebook which were victory points.
So is this the best way to resolve the problem?