A 40% stake is a lot, but considering the high risk, you might have to settle for it. You might be able to buy back equity in the future as the invested is paid back.
I would rather put the game off than offer up a 40% stake in the company. If it were say a 25% stake in the game, that would be a different story, but a 40% stake in the company is waaay to steep a price to pay for the funding.