Does this scenario play out often enough that planes need to leave their assigned altitude when a strong tailwind is heaving them along the north atlantic?
No.
That abrupt a decrease in wind would be accompanied by significant turbulence, and would be very short-lived. While it is theoretically possible, it is very rare that an airplane cannot accelerate faster than the rate of decrease in headwind at high altitude. It would be exacerbated if the airplane was flying at maximum altitude for its weight, which would leave it with little excess power and little stall margin. Most of us avoid that situation if turbulence or wind shear is forecast.