I'm so sorry to hear this has happened. I understand as an artist myself how frustrating it is to lose all of the work you did. Sometimes however, pushbacks like these can cause us to create even better works than what was lost. Don't lose hope! Use this as an opportunity to do something different, change designs, have fun with new concepts, and see if there is something you can do that you hesitated previously, or old scrapped concepts that may work better in your favor. Sometimes being stuck with strict adherence to old concepts can burn you out. You aren't starting over, you are building off of things you already created and now have more knowledge as to how to move forward.
That being said, I do also understand if you reach the point of knowing when to step back or put the project on a backburner. Take a nice break and or maybe start on something else for a while until you are ready to return with renewed vigor. There is nothing wrong with stopping a project despite fan outcry, because your sanity and health is first and foremost. It wouldn't be a failure to do so because creators cannot create if they are burnt out. I wish the team all the best! I know you all are working hard and I can't wait to see what comes of it in the future.