I've never taken a sleeping bag but have suffered poor sleep (I get very cold, even with my natural insulation). I was tempted to try Lael's method which is just to take a sleeping bag and throw that straight down but I reckon sans-pad a lot of heat will be lost to the ground.
It doesn't usually rain much on TCR, ie in Eastern / Southern Europe in August.
If it is raining most people either find shelter / hotel or keep riding until it stops.
I wouldn't be out in the rain. My bivvy isn't waterproof anyway.
If I had a more durable bag, that would be a good combo. I normally run the pad in my bivvy though when I'm doing audax to protect it a bit.
I've never taken a sleeping bag but have suffered poor sleep (I get very cold, even with my natural insulation). I was tempted to try Lael's method which is just to take a sleeping bag and throw that straight down but I reckon sans-pad a lot of heat will be lost to the ground.