I don't think I have been in serious situation like that but maybe I misunderstood your post. Though I did encounter serious bug with my new concept but fortunately managed to solve it. Now, I'm thinking on what to do next with this concept.
As for pushing forward or reconsider it, well since I'm used to with gamejams, I am used to going with the former to save time. Instead of failing my submission, I rather push forward with whatever concept I had in mind when working on my submission. I know that I'm going to enjoy the implemented concept so it's worth the risk.