To be honest, I have no way to quantify the danger involved with eating food out of a pesticide laced plastic bag. I had some rice that was packed in a garbage bag once, and just as an experiment I ate some rice from the middle of the bucket which had not been in direct contact with the garbage bag and nothing bad happened. I didn't get sick (that I could tell anyways), a second head didn't grow out of my shoulders, and it tasted just fine. If I was in a survival situation and had to eat the rice, the possibility of poisoning myself slowly from cumulative exposure to pesticide would rank much lower on my list of survival priorities than dealing with the immediate threat of starvation, so I would eat it. Remember too, pesticides are designed to work on insects. It takes a lot more pesticide to effect an animal or a human than it does to kill bugs. All the horror stories you hear of people being harmed by pesticides are from people who have an occupational exposue to pesticides and have been exposed to high concentrations of it over the course of years.
The only reason I did toss the rice and replace it, was because I had the resources and the money to afford doing that. If I didn't have the money for it, I would still have the rice today and I wouldn't lose any sleep over it.
The point of all this is that you should avoid making this error to begin with just for the sake of knowing that your food supply is pristine, but I don't think that it's necessarily a fatal error.
As far as washing the rice off before cooking and eating it, that sounds like a good idea to me even though I couldn't say definitively that it's necessary.
I don't know if pesticides would boil off in cooking.
