As unmined bitcoins get lesser, the difficulty and the time needed to mine gets higher. So unless technolgy advances on par with the speed of mining, then we will see the end soon. Otherwise, years or even decades more will be needed.
Even after that, miners will not decrease as the earnings from transaction fees alone is good enough to keep them going. We all know the number of people who knows and use bitcoin and it will just increase as rapidly as it used to.