I have crewed airplanes that have had bird strikes and hail strikes. The worst I saw caused extensive damaged to the aircraft from a large flock of birds smaller than Canada Geese, crushing the nose radome, damaging the leading edges of the wing, multiple engine impacts, and other damages. But, the airplane was controllable and safely landed. Hitting a flock of large birds, like Canada Geese, does increase risk but when thinking of drones the general concern is for one vehicle to impact the airplane unlike a flock of birds. Loss of a single engine, damage to a flight surface or other such damage should not make the airplane crash but allow for a timely, return to base or completion of the approach. If someone launches an attack with multiple drones then the outcome could be much worse.
As stated in the information posted by TWA884, a loss of engine thrust was possible if the drone impacted the fan blades of an engine at high speed (high power settings like during takeoff). Again unless multiple impacts happened I believe the aircraft, while damaged, would still be able to make a safe landing. Airplanes are much tougher than people believe and can withstand a fair amount of damage and still be flyable.
In 2001 there was a mid-air by a Chinese military jet and a U.S. Navy aircraft. The Navy aircraft was severely damaged but was able to land. The outcome for the Chinese jet wasn't so good. This represents a much larger impact than a drone and gives and indication of just how tough airplanes are.
Video before the midair.
I'm not saying there is no risk, but I believe in most cases an aircraft vs drone mid-air would allow the aircraft to land safely. There certainly is some risk of shooting down drones over potentially populated areas since some many airports have lost safe buffer zones due to population growth in the area. I don't have an answer of drones flown in the vicinity of airports but would be very hard to convince that shoot downs are the way to go.