How would losing their spell book affect an NPC wizard-sorcerer multiclass?

Question

I’m currently DMing a long-running campaign and trying to plan a small quest to save their wizard NPC friend from an evil-wizard’s abandoned lab. My initial thought was to have him lose his spell book to render him more-or-less useless. Unfortunately, I remembered that I gave him 2 levels in sorcerer when making a character sheet for him and my players know this.

Thus, the question: Would taking away this character’s spell book render him helpless and in need of rescue? Or would he still be able to use all of his spell slots to get himself out of trouble?

Answer 1

Any Wizard without their spellbook isn't automatically helpless

The core issue with this plan (going by rules as written) is that a wizard's spellbook is only used for learning and preparing new spells. A wizard that loses their spellbook will be unable to prepare new spells, but will still have the same spells prepared. There's even a specific clause (and price) for writing these down in a new spellbook should you lose the old one (see the Your Spellbook box on page 114 of the Player's Handbook, under Replacing the Book). And they'll always have their cantrips, no matter what happens to their book.

So even without sorcerer levels, a wizard bereft of their spellbook isn't rendered helpless, unless they prepared a very specific array of spells before losing the book. Adding sorcerer levels means they get additional spells which are known entirely independent of the book, and can cast all of these spells using the same slots (PHB 164). They even get more cantrips.

The only way for a wizard to be rendered helpless this way is if the exact spell they need is in their book, but not prepared that day, but I don't know what spell that would be.

Answer 2

No, it would not hinder them much at all

Even if they were a wizard with no other classes they would still retain all of the spells they have prepared. A wizard only needs their spellbook to swap out their prepared spells and to make use of their arcane recovery ability.

It would really only be a problem if the spells they had prepared were insufficient to help them out. Like being trapped on a small island surrounded by lava/water filled with piranha and not having any kind of spell to help them escape.

Taking away any spellcasting focus/spell component bag could hinder them a bit as they'd be unable to cast any spell with a material component.