That is a bunch of bovine excrement. Assuming your account was in good standing programming your number into a new sim is easy. Providers do it all the time for people whom lose or damage phones.
Now if the account went into the rears and or was cancelled then the number is gone and you are hosed and like permanently lost the account and will need to create a new one.
Apparently you didn't read the whole post. I never said they were valid forever, even stated a couple situations where the number would be lost.The bovine excrement is your post. I work for a mobile company and there are certain terms to be complied with for number retention. Numbers are not valid forever. If they are not topped up or used for a certain period of time, they will be recycled and allocated to a new user.