You won't have broken the router
Holding down wps as you described restores the settings back to factory default, so you might want to leave that to last, unless you don't mind restoring them yourself. That said, given you can't know what might be corrupted, I'd probably restore just for peace of mind. I think any of the options you suggested are sound, Pulling out the power cord, and switching off the main power switch are the same thing - you're breaking the power supply into the router (unless you mean uplugging the adapter from the wall, which might have a slightly different characteristic eg power tailing off rather than a sudden break), though of course it's best to use the switch.
I think when this happened to me when I first got the router, I reflashed with the larest Asus firmware and then reflashed with the latest Merlin firmware, but I suspect whatever I'd have done would have had the same effect.
Remember: you restore/reset to factory default settings AFTER flashing the new firmware. (There may be no harm doing it beforehand as some people do, provided you also do it afterwards as well.). And as an alternative to restoring to factory default settings using the wps button, you can also do it from within the web GUI, though, for those occasions when you can't access the GUI, the wps method is ideal.