Yikes!
Yeah, what a bummer that would be after working so hard! If you catch them in the process of having the heart attack, you can go ahead and slaughter them quickly. But if they die and you find 'em dead and stiff, well...that's that. You can't process 'em and you loose that investment of time and money.
I've been watching them carefully all this week...moved the tractor up closer to the house and everything.