What happens if 1 company or person controlls over 90% do miners move to another coin or just use bitcoin?
If one party owns 90% of the network bitcoin is effectively dead, at least as it was intended. It's called a 51% attack.
Some miners mine to support the network and will even keep mining at least for a while when it's no longer profitable, betting the future value will make up for it. The difficulty makes sure it will always balance itself to keep mining a relevant operation if the network isn't completely compromised.