I think right now, the only conditional send options you have are the following:
I feel like with some creativity you could probably do this by linking the criteria with a yesno field (i.e. (total_sales > 400000), adding that yesno as a filter, and selecting either yes or no on the Look. Then, scheduling it to send only if there are results would provide that conditionality.
I should also mention I’m pretty sure Looker showed a slide deck indicating that proper conditional scheduling is in the pipeline, which I’m very excited for!