Yep, which brings us back to disarmed-at-0-hps. Or Disarm as an alternate skill check to force surrender, similar to the existing Intimidate option.
If you're not defeated when disarmed either a) you can keep fighthing effectively unarmed or with a backup or improvised weapon or b) you fairly quickly re-gain your original weapon, perhaps forced to go on the defensive, move/dive/whatever to retrieve it.
About that, yes. Weakened would reduce damage on a hit more than re-calculting everything with a back-up weapon or improvised weapon or unarmed strike; and, but, even with inherent bonuses going, it would probably hit more often... so it's a fair aproximation.