I wouldn't be against McInnes being Scotland manager at some point in the future. I think he'd make a good international manager. Share your worries that Davidson would be in the frame if Clarke left, though.
I've always liked Steve Clarke but have to say I think he got quite lucky in that the Nations League was introduced during his tenure. We finished 9 points off a Euros spot in our qualification group and if you look at the other groups, that was by far the biggest gap between 2nd place and 3rd place in any of them. Craig Levein, Walter Smith and Berti Vogts all came closer to getting to a finals through their qualification groups, and perhaps would have got there if they'd had the Nations League route to fall back on.
That's all four of the countries who qualified through the Nations League route now knocked out at the group stage (although Hungary gave it a bloody good go in a ridiculously difficult group). I just find it a bit pointless - although I'm perhaps biased because I think there's way too much international football on the calendar.