Less miners means less competition, so any of left miners can get reward more often, you have to take that into account aswell
Inverse correlation, if 1000 people mine BCH, then every single one of them can get some 1/1000 if 10 000 do chance goes down to 1/10 000
Heck if so many stop mining BTC, I will start mining it
Yes but it is possible that you will run your mining operation alone. And as far as you do not mine 2016 blocks for a difficulty adjustment you are not getting much at all.
If 2016 blocks can't be reached anymore, I guess it is still possible to hard fork to not leave all the owners stranded? Just a thought.
We already had a hardfork on 1st of Aug and the next one is planned in November.