I think key parts of their plan were revealed in the war-and-peace ransom note, which I firmly believe PR wrote.
First, is the line that mentions "bring an adequate size attache" to the bank. I believe at the time the RN was written, the plan was to get JB out of the home in the blue suitcase that reportedly belonged to JAR. It doesn't matter that she wouldn't fit inside, I think that was PR's plan.
Next, notice that the RN states the kidnappers would call between 8 and 10 "tomorrow", with "tomorrow" apparently referring to December 26. The RN then states "if we monitor you getting the money early, we might call you early to arrange an earlier delivery of the money and hence, a early pick-up of your daughter". This line seems to encourage John to get going early....what PR failed to consider when she was writing this line is how many banks open before 8 AM?
But she was thinking ahead. I believe she thought this line would give John an excuse to get the body out of the house very early. I should mention here that I believe it's significant that JR is the only one who'd taken a shower, as I believe he did the clean-up and most of the staging, while PR was trying to pull herself together, script a somewhat believable fake crime and write the RN. Anyway, I think PR wrote the above quote from the RN as an excuse for John to leave very early in the morning, and I believe she wrote line about the attache to give him an excuse for leaving with that suitcase in hand, should any neighbors happen to see him leaving.
I think the plan was for JR to leave with her and dump the body somewhere that it would be quickly found, then drive to the bank where he'd be waiting when bank employees get to work. He'd then go inside with the blue suitcase to make sure bank employees seen him with it. Then stop at a pay phone (remember those?) very close to where he dumped the body and place a call to his house. That way if police trace calls into the home, they have a good lead on where to go. JR would then dump the blue suitcase, (which would have her hair, clothing fibers, DNA, blood, whatever else inside) and go home.
Once JR returned home, all they'd have to do (in theory) would be call police, and show them the RN. They'd then state JR had went to the bank and gotten the money, which could be corroborated by bank employees, and claim they'd received a call for him to drop the money, which could be verified by John's pay phone phantom call should a trace be made. Then claim that JR took the money where he was told, but they never got JB back.
This is my personal theory that I came up with after studying what I could find on Patsy. I believe, for one reason or another, that Patsy panicked while John was showering before this plan could be set in motion, at which time she called police...and everyone she knew.