Is there still a significant number of miners with the equipment required to process proof of work? Is there a danger in that the cost to run such equipment being so high that it leaves very few miners able to afford to do the proof of work, and thus it leaves only one or two miners and introduces the possibility through collusion to start manipulating the blockchain?
The number of miners is actually still increasing, so you should not be worried.
Also if miners would leave, after a number of blocks the difficulty would adjust, so the mining will become more profitable for the remaining ones.