Over 95% of my revenue comes from organic search
Yay! Nice work! You are one of the few remaining businesses who are able to do this.
My ROI on AdWords is roughly zero.
Me too. I just did yet another experiment to convince myself that it is almost impossible for a small biz, a retail reseller, to make good money, even any money, using Adwords.
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?
My opinion on this is "NO". I would turn them off with confidence. I think that you will still get some of the sales that are currently coming in through Adwords.
First, could Google retaliate to my reduced ad spending by dropping my rankings?
I don't think that they will do this. I don't think that Google is vindictive in this way. Several years ago we used to run Adwords quite a bit. We would turn the ads on and off for employee vacations, sick days, and when our retail stock was low. Organic rankings never changed a bit.
Second, will searchers think differently about my organic link if they don't also see the accompanying paid link on the SERP?
I doubt it. I think that lots of searchers skip over the ads. Any searcher who runs ad blockers probably skips over the ads while cursing. I think that dropping Adwords might increase the profit margin of your business because it was probably depressing the profit margin while you were paying for the ads.
I think you are a smart guy because you have done the math to figure this out. Most people who run Adwords are blissfully losing their shirts and pants.