Sorry if this has been asked before or is clear somewhere, but we had a disagreement at the table - do sneak attack/quarry dice get maxed out on a crit as well?
No, you roll the dice of the extra damage.
See: "Critical Hits" on page 278 of the Player's Handbook
To sum up:
You MAX
[W] damage, except any [W] damage that only occurs on a crit, like high crit.
any damage that says "add XdY damage to the attack" or "the attack deals XdY extra damage".
You don't max
[W] damage that occurs only on a crit.
any damage that says "once per day when you hit, deal XdY damage to the target" (like fiery weapon for instance).
Other damage that only applies on a crit (like the paragon feat that applies 1d10 damage on a crit).
Any ongoing dice of damage.
Any other form of damage that says "when you crit...".
So, back to the OP:Sorry if this has been asked before or is clear somewhere, but we had a disagreement at the table - do sneak attack/quarry dice get maxed out on a crit as well?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.