This ties to how strong the reward is. You don't need 'full clear', but it is a huge difference if you get a brick, half a brick or 1.2 brick.

To be strictly technical, there are no 'retries', only 'continues'. It would be fun to tweak your team trying to beat the tower for high score, similarly to how you can do with dummy events. But here, not only you have very limited set of keys but also you can't attempt to get a better score on the same map again.