YC is a minority stake investor, not their boss or board member. It seems that what you are looking at is a breach of contract where the company did not delive

YC is a minority stake investor, not their boss or board member. It seems that what you are looking at is a breach of contract where the company did not deliver what they agreed to deliver. If the company ran out of money, they are probably a dead company/ bankrupt and have or will shut down. They are unlikely to be able to return the money or deliver, and you could end up either trying to sue a company that is dead and/or pierce the corporate veil alleging fraud. Check with your lawyers.