Yeah I've actually played duo with a friend who only just started playing RE6 and can't do things like counters or cdg. We almost made 150 combo on our first try. I simply let him start killing right off the bat and I collected all the time extensions. I honestly don't know how hard it would be for a duo player to transit to solo, I think it would really depend on how good a route you have for the entire map.
As for getting grabbed etc, as a solo player you have to come up with proper strategies for dealing with those by yourself without dropping the combo. It's unlikely to play an entire round without getting hit a few times, so once you've learned these skills, they translate well to duo. For example after getting knocked down shooting from a lying down position is faster than getting up, cancel long reload/rechamber animations with a weapon swap, incendiary are instant kills for most normal zombies/javo and almost won't hurt you at all, flash grenades put most javo in cdg stun, etc etc.
