First & foremost I'm glad you're both OK.
I started racing MX at 11 & turned pro at 16. in my 20s I also spent some time racing speedway with a steel shoe on my left foot & power sliding the rear while counter steering the front. I live in the Colorado Rockies where it can snow in July and road gravel, sand, & boulders can appear out of nowhere at any time. Last fall on a 65F degree day, came around a north facing corner & narrowly missed a patch of ice. There had not been any snow. Just some water that ran across the road & night time freezing temps on this north facing corner left a 3' x 2' patch of ice.
When I was 18 I stopped at a stop light. When it turned green I turned left and laid my bike down when the front tire hit a 3" puddle of motor oil that leaked from a car. I was going less than 5mph, no damage, lucky there wasn't any on coming traffic to run me over. I didn't see the oil cause I was looking ahead & scanning for oncoming traffic.
My point is, on a road bike we all must expect the unexpected and the reality is road crews can only do so much.
You asked "what would you do?" I don't know. When I ride, my body reacts without thinking. Sometimes I accelerate. Sometimes I back off, stand the bike straight up and brake hard. Sometimes I do both. What a rider does is dependent upon his/her skill set. if you have to think about what to do, it's too late. I definitely tend to ride defensively and try to keep to the right track on blind corners. That said, zipping through twisters on my Hyper can be irresistible!
If you're really serious about improving riding skills & reaction time to handle the unexpected, then working with a pro on a closed course might be an option. I know of road racing, MX, and "drift schools" that are perfect for acquiring better riding skills and becoming a safer rider. Great of you to ask what others would do, but applying the techniques takes practice.
Again, glad you are both OK. Very fortunate that your run in was not with a car! This could have easily been any one of us!