If the investors were fully aware this is at risk and they backed you because of the team and not the product/market then I'd use the remaining cash to build so

If the investors were fully aware this is at risk and they backed you because of the team and not the product/market then I'd use the remaining cash to build something else where you are the first customer and start over. Reduce the team to just the co-founders, 100k is still a lot of money for a team of two or three and you can probably afford one or two more experiments.