[Gulnyr]

I agree that a spellbook is often a greater loss than other equipment. The main gist was more that the primary tools of any profession should be vulnerable in dangerous situations than that every tool should be treated equally.

The backup actually seems like the default to me. Would an adventuring mage take her one and only spellbook with her? Why not leave the full book at home, safe, and take a smaller traveling spellbook on adventures? Maybe she can't scribe as many spells in it, but it means the loss isn't as great should it be lost, plus it's lighter and smaller. That would create a similar 'going to buy a new one' situation that other professions would deal with.