Salutations. Nice hair.
I´m not sure about this, so this response is more about telling you this fact than anything else.
Anyway, validations based on foreign licenses expire once the base is expired, that´s true. The "I´m not sure" part comes now: I GUESS that if you want to have a FAA license, a... say "complete" license, you´ll need to pass the writen and flight tests again. Not saying that you´ll need to get again your 45 flight hours as soon as you already have them, this is sure again, but the tests.
The unknown part for me about this question is if they will require you to fly some hours in a FAA school before you get it. In Europe you are asked to take a 5 flight hours course before attainning a "complete" JAA PPL when you already have a foreign one. In the USA...?
Be sure that you have many people here that can ask it "from inside"
Salutations. Nice Hair