How powerful is a high-level PC with barely any or no equipment?

Let’s assume your PC or even your entire party has crossed a high-level spellcaster and his minions the wrong way, or was overwhelmed by an army of guards. You are stripped of all equipment save for some clothes on your back and get exiled into the wild rather than imprisoned.

How much power – specifically combat power, as your skill levels would be mostly unaffected – do you lose? A Wizard cannot cast spells of 1st level or higher without a spellbook, but can still cast Firebolt for 3d10 or 4d10 damage; a Fighter can only use their fists, improvised weapons or grapple, but likely has STR maxed at this point, so that would still be 6 flat damage x 3 minimum per round; your armor class is most likely diminished to 10 + DEX modifier.

On the other hand, a Monk would probably do reasonably well even without equipment or magic thingamajigs he acquired thus far.

To substantiate “high level”, let’s say we’re dealing with a character of high Tier 3/low Tier 4, around level 15/16, so no access to e.g. Wish spells.