Damien

Well it's been subject to a number of production delays that were chalked up to Marvel adjusting it's releasing schedule for the new phase of films. Maybe that wasn't the reason....

I highly suspect that they knew he had cancer. It's almost a certainty they knew as he would have various medical and insurance checks for the role and it would have been hard to keep his treatment secret during the filming of Black Panther and Avengers.

So they probably already do have an outline of what they intend to do.