Why canceling the halving, i think it is programmed on that way that when the next 210,000 blocks are reached (on this halving it will happen on the 420,000th block), miners can not decide to approve or vote to cancel or not the halving. Let's see what will happen in less than 2 days.
Technically they can (if the majority wants to). On the other hand, they will never do something that would destroy their business. So, don't worry!