Leaving aside the question of automation (does HAL 9000 get to push the button?), there really isn't any alternative. The mission as a whole is fighting the Poisson distribution of encountering random objects in space. The probability of hitting one is very low but not zero. Unless the system is magnetic-ramjet powered, the fuel is finite. Ultimately the choice is between stopping at your predetermined destination or waiting until a rock turns your entire world into a sparse cloud of floating debris. It's like the "what do we do if Earth gets hit by a meteor" question but much, much more acute.