MechaPilot
Explorer
It's fine for a couple encounters. Just don't keep him without a spellbook for too long. It's a serious limitation on the class, which is designed to be flexible in spell preparation. Besides, when he levels up, how would he gain and prepare new spells, which is a core feature of the class?
So a good rule of thumb is that the character should get his spellbook back by the time he levels up.
I had to look into wizards without spellbooks for a homebrew setting where writing and literacy are nearly non-existent; and I agree that it's a very serious limitation as the character grows.