Typically, a miner will sell (all mined coin or may some of the coins as Vann said) or hold the coin for some period. So, that wouldn't affect increasing value of coins, Dropping coin value, may Yes (if miners sell coins in the large amount). Miners who bought some coins (that was a different story).
The right story behind mining was:
Miners that doing mining will keep health and secure coins network. And also getting some profit