Here's what happens when you try to damage/destroy a magical tome:
|Reaction to attack
|How to destroy book
|Cast Raise Dead upon the book.
|Cause the book to run out of magical ink. This could take awhile because it has over 100 blank pages in this section.
|The book is completely impervious to damage. Nothing can tear a page or even scratch the cover.
|Getting the book wet will cause the ink to run and will effectively destroy the book.
|The book gets angry. It begins casting the spells within its pages. You'd better make a saving throw...
|Befriend the book and convince it to cast erase upon it's "heart page".
|The book summons allies from -- (1) elemental planes (2) abyss (3) nearby (4) other dimension -- to defend itself.
|Seclude yourself in such a way that the allies may not be summoned (or are summoned into peril) then destroy the book.
|The book splits in two, making two copies of itself. One copy promptly teleports away.
|Destroy the book in such a way that its duplicate is also subject to the damage and the damage is constant and ongoing to prevent runaway divide and teleport behavior (Mt. Doom anyone?)