concerns about driving with cracked headers. A couple of questions...

I put 50 to 100 miles on my 97 F 355 before I realized my left hand manifold is cracked. What gave it away was the dust in the engine bay. I had some throttle hesitation the last two times I drove. So my question is what are the chances that I did significant damage to the engine? It has been parked since I realized the problem and I am awaiting new headers to be delivered. Quite concerned about this so I started a new thread even though I've asked the same question on multiple threads. Thanks ...i am obviously quite concerned about this issue...