It wouldn't make sense for bitcoin to kill fiat currency since it is entirely backed by fiat currency.
Face it, if you couldn't exchange bitcoins for dollars, not one single person would bother with them. Just go to any thread where someone is scamming/selling something. Everything is translated in US dollar value.
This is only partly true. I personally would enjoy taking USD out of the equation.
I would accept
only bitcoin, period.
All money is based on trust in a system, ability to be recognized, and usability. In this era of transition, digital money is an easy choice to make.
Just make it. 
I suggest seeing
this → (
http://www.youtube.com/watch?v=9LaSrxtWfgc ) and making a final decision.