It is kind of intriguing the Death Note never runs out of pages...
How to Use: XXXI
The number of pages of the Death Note will never run out.
Since it's made of an unknown matter it's not really that difficult to believe, but we didn't really see the effects of this rule in the anime, which I guess could be more important than most of the rules (unless you show me some other point of view in the answers), by analyzing:
The thickness of the Note should increase:
By assuming that the number of pages will increase every time you use the Note pages to make it endless, we would clearly see that the Death Note will get thicker, since the number of pages is rising, and we would clearly see that the Note of Light would be too thick after his long years using it.
The already written pages remains:
We could also deduce that the pages that are already filled do not disappear since both L and Near did analyze the names written on the Notes and the names of the dead victims as another evidence of the conviction.
Now as a question:
We know that the user can rip some pages from the Note to use them later, now what would happen if the user rips all the pages from the last one filled to the end cover of the Note for using them later? :
- Will it be judged as destroying the Note?
- Will it be judged as ripping some pages?
If 1), the Note will be rendered useless.
If 2), would other pages appear in the Note? In case they appear, could the user keep ripping off pages and giving them to hundreds of people making Kira everywhere? Why didn't Yagami Light do such a thing as becoming the master of the page users and the only one knowing their names in case they disobey him, and as a result, creating an army for himself made of the Kira fans?
Check also: Why is there an entire Death Note if only one page is enough?