I doubt the buyer cared one way or another whether the previous investors got their $800k back or not.
I'm guessing it's more that the buyer was only prepared to go to 4mil, and the _seller_ had run their numbers and came to the conclusion "4mil minus that $800k isn't enough to secure my families future, and I'd need to walk away from the deal unless they agree to forgive that $800k" so he asked them, and they agreed.