let's see. Crossing interstate lines to conceal a crime? Tampering with evidence? Fleeing a crime scene?
In reverse order...
They didn't charge Plaxico with "fleeing a crime scene", yet he left to go to a hospital. Doesn't an ambulatory accident victim get to choose what hosptial to go to? Is there a law against crossing state lines to go to a hospital?
But, moreover... The crime was illegal carry (as opposed to being an idiot and shooting oneself). If illegal carry establishes a "crime scene", every run of the mill thug in the city, should be charged with "fleeing" when he crosses the street and establishes a new crime scene. Or each time he returns home with his gun he has left the crime scene of the street. Perhaps the next day he doens't carry, but the day after that he goes out armed and establishes a new crime with its scenes. Yet they don't charge the guy with these crimes, even to plea-bargain them away.
What evidence would be tampered with by going to PA? Was evidence tampered with by going to the Cornell Medical Center in Manhattan?
I suppose, with witness testimony, they might get a fugitive warrant for leaving the state, but there is a good chance that he'd be back in NY (or at least at home in NJ) before it was executed. And it would probably be easy to get a good enough lawyer to make fugitive charges to go away. A case could be made that being on TV every week would seem to negate any intention to be a fugitive.