An
interesting thread at the Amazon message boards was pointed out to me, started by someone whose account is 'on hold' before closure. That person explicitly states in one post in the thead "One point that I would like to clarify is that Amazon has told me that I will continue to have access to my books."
It's the registration of new devices that might not be possible.
And while it's hearsay, another poster in the thread said "Of the 5 people I have known that have had their accounts closed, one had no digital content, and the other 4 could not post in the threads, nor could they make purchases from Amazon, but they did not lose access to their digital content."