Playing a fighter or a barbarian, it's a cool image to have your bone axe shatter against the hide of an Ankylosaurus, or your wood and leather armor torn to shreds by a pterodactyl. Then making new stuff out the Ankylosaurus and pterodactyl. . .
Does the wood wand shatter? The stone tablet spell book? Wouldn't a character just make or purchase 30 wands? Wouldn't a spell book breaking be much more consequential than an axe or armor?
How would you build the idea of breakable, prehistoric items into prehistoric spellcasters?
If I were playing a fighter who was fighting an ankylosaurus, and my bone axe shattered against its hide, that would mean that my spear had already shattered against its hide. And my bow had already run out of arrows. And it had already sprung, and survived, the traps that I had set for it. So no, not cool!
Prehistoric wizards had one spell: create fire. And they were pretty popular girls to have around.
Seriously though, I would expect wizards to have some pretty low-pizzazz spells and/or magic items, given the surrounding low-technology. Strangely, their tools have been seen and used as late as the 20th-century (?): animal bones, skins, and innards. These don't break, because wizards are smart enough to not go bashing their chicken ribs over the heads of ankylosauri. Instead, when the magic of one "fails," the wizard declares that its magic has run out, and acquires another chicken rib.
Alternately, magical implements are made of the softer animal bits, which "break" when the bit starts to decompose.
For weapon breakage, I'm a big fan of a simple rule:
- You can choose to sunder your weapon when you take the attack action, if the attack hits, you maximize the damage of the weapon for that turn and then you can use the weapon until it is repaired.
- You can choose to sunder your armor, when you do so, you reduce de damage taken by the amount of AC granted by the armor (ie: 13 for an hide armor) then the armor's AC becomes 0 until repaired.
- You can sunder your shield to turn a critical hit into a normal hit. The shield becomes unusable until repaired.
Not what I'd call a simple rule, but a good one nonetheless! (Should the weapon rule read "can't use the weapon?")