Wow. What chapter of MENSA do you belong to?

Spot on!
While it could be argued that the failing heat shield might have been pre-planned to assure that no one would be around to blow the secret wide open, I seriously doubt that was the case. The heat shield separating was most likely a complete surprise, and - as Kelloway puts it when talking to Mrs. Brubaker - after the heat shield seperated it was over in less than ten seconds.
It was a freak accident that anyone would have had little to no chance of saving themselves from.

Aren't the life support system and heat shield two separate things? I thought the heat shield failing was a complete surprise to Holbrook's character and that he legitimately thought he would have the astronauts survive and be placed in the capsule once it landed.

Didn't they originally say they changed it's course so they had time to replant the astronauts miles away? The course change could have made a difference.
Or it was supposed to happen on this fake mission to keep the astronauts quiet permanently.

I think maybe there would HAVE been some effort to get a replacement heat shield or entire re-entry capsule up in earth orbit for them to use when they got back. Plenty of time to organise that.

Of course they would, but then they would have died and been rightfully celebrated as heroes, pioneers and basically modern day supermen.
As things went though, they will instead be murdered as mere inconveniences.