If anything is likely to be discontinued it is the 1.3x crop bodies like your 1D MkIIN. Canon could easily decide to just go with EF-S and full frame EF bodies. The two systems should meet everybody's needs. The 70-200 f/2.8 IS is an EF lens, so it can be used on either system, whichever way you decide to go in the future.
IS can be turned off using the switch on the lens barrel and the lens can be used as a non-IS lens. If the IS mechanism should happen to break, it should be no different from turning off the IS switch. The only likely problem would be if the moving element in the IS system came loose when it broke and flopped around when you moved your camera. That could have a negative effect on framing shots or introduce blur if if moved during exposure. It is not likely that it will break, and if it did it would be more likely that the gyro mechanism just failed, not that the lens element would come free.