It is an interesting dilemma for the TV adaptation, the question of how long Gilead endures. I know it's in the book that it lasts for a very long time, but for the purpose of a ten-series run on TV, surely that needs to be changed. I think Atwood would agree to that.
Also the book was written in 1985, and we're now facing resurgent fascism, so it's urgent that we look at how fascism rises and how it can be defeated if allowed to gain power. I can't see that Gilead would have been sustainable for as many years as is implied in the book.
I found The Power disappointing, and there are blatant rip-offs from The Handmaid's Tale in it, such as the ridiculous bookending from the future - which the publishers wanted to take out, but Alderman insisted on keeping in.