Your retinas are sensitive to light because light causes certain molecules (rhodopsin, I think) to change form and release energy. This chemical energy builds up in your photoreceptive cells and is then released as a neural signal. In other words, you would just see the light dimly, same as if the strobe were going really fast. What's interesting is if it's going a little slower than the fastest your eye can make out - the light seems to turn on and off slowly as the strobe and your eye go in and out of phase.