You people have to learn how to use the search function. There are more than ten duplicates of this thread.
The price would rise, the miners would start pumping their saved up bitcoin so the double, so the 12.5 BTC is worth what 25 BTC used to be.
What exactly do you mean by "pumping their saved up bitcoin"?
Also, miners are a small part of the market, and after the halving their part will be even smaller.
it depend, i can argue, that they are holding a considerable amount of bitcoin, and they can control any exchange easily, especially chinese miners
so no, i believe they make up for quite a threat in the market scene