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.