Over 95% of my revenue comes from organic search; less than 5% comes from AdWords PPC (all other sources account for about 1-2%).

My ROI on AdWords is roughly zero. It's negative if you include opportunity costs.

My question is: if I pause all of my AdWords campaigns, is there ANY chance that my organic rankings (and organic click-through rates) will suffer?

This is really two questions. First, could Google retaliate to my reduced ad spending by dropping my rankings? Second, will searchers think differently about my organic link if they don't also see the accompanying paid link on the SERP?