If you start out trying to enforce the contract as agreed and think that means that Patrick is 100% responsible, then Patrick next has a claim against his investors for the harm their mistake caused him. This claim would offset their claim against him for making the same mistake. You end with them needing to split the losses.
Wait, so if someone breaks into my house and is accidentally impaled by the set of spears that I by mistake only very loosely fastened to my ceiling with a string that too goes across my floor, then that guy has a claim against me?
Unfortunately, yes. You can find dozens of lawsuits where someone is injured while trespassing with intent to steal and successfully sues the property owner. The most famous, Bodine v. Enterprise High School, involves someone trying to break into a school who fell through a skylight and successfully sued the school. (Successful in the sense that the school ultimately settled for a six-figure amount.) There was a great case in California where a man accidentally ran over the hand of someone trying to steal his hubcap. There was a successful recovery (around $75,000 or so) in that case.
There are two big differences between those cases and this case. In those cases, there isn't the same mistake made by both parties. And those are tort cases, not contract cases.
A reasonable justice system would, I think, prevent criminals from recovering from their intended victims except in very exceptional circumstances. See
http://en.wikipedia.org/wiki/Trespasser#Duties_to_trespassers (If there was evidence that Patrick was dishonest in his communications with his investors, this common mistake argument would evaporate. It is predicated on roughly equal fault on both sides.)