[Jack Wilson]

What if he goes back in time and gets killed? How will he invent his time machine?

[surfer]

One time when I was traveling at the speed of light, I turned my headlights on...I still don't know what happened...next thing I knew Clinton(i) was the POTUS.

[Stavka2]

If he goes back in time and gets killed, it won't matter since he already invented it. If he goes back and gets his younger self killed or one of his ancestors before that ancestor can reproduce...he'll cease to exist instantly. Love those paradoxes.