Don’t sell, don’t give, don’t walk away. Stand firm. This was a binding agreement they can’t get out of. You have all the power here. You know you have something. They have established a lower bounds on its value. It’s way more than 40% of 400k.
Best of all. Don’t let your customers know it’s founders are going through this. It’s obvious, but make sure you keep your cool and composure. It will pay off in the long run.