Perhaps the task needs to be completed in a certain number of rolls. If you haven't gathered the required number of successes with the number of allowed rolls then you fail the task. For example a task that requires 3 successes in 5 rolls would indicate a complete failure if after 5 rolls only 2 successes were gathered. I think that Pathfinder has a system like this.
I think I used something like this in Curse of the Emerald Tower Part II.
