What is it that you are specifically worried about?
- If you cancel all your accounts that have Amex points and fail to transfer them, kiss them goodbye
- If Amex closes your account for fraud you may get 30-60 days or maybe not
- If you cancel a card in <12 months Amex may claw back points (per terms of application you signed)
- I have never seen a pro-rate AF except on a product change
If you are worried about involuntary closure then transfer your points to an airline partner. Pretty simple.
I am not sure why anyone would voluntarily close all Amex accounts when there are no-fee options that allow you to retain your points (e.g. Amex Blue Biz Plus) assuming you can get a biz card.