The T-Rex lived in the Cretaceous period, not after the Cretaceous period. T-Rex fossils are pretty much exclusively found
before the extinction event, as is evidenced by the
K-Pg boundary (and in the specific case of Tyrannosaurus we have only "a few dozen" such skeletons anyway.
These are not the only types of events that can lead to fossilization. Do you think animals jumped into tar pits?

In any case, I can't find any evidence of this velociraptor fossil that was preserved "standing over" prey or "munching" on it. The best I can find: "...two hatchling Velociraptor skulls that were found near an oviraptorid nest in Mongolia (the eggs may have been a meal)" (
source).
Or are you talking about this one?
It's an incredibly rare find, and the prevailing theory is that they were swept up in a sudden, massive sandstorm, or the equally-sudden collapse of a sand dune (explaining why they were encased in sand). If you believe that this is impossible, witness the evidence from Pompeii, where the lava and ash that preserved its citizens came in at 100 mph, and resulted in scenes like this:
http://peripateticbone.files.wordpress.com/2013/03/body-2.jpg (click to expand)
http://static.environmentalgraffiti.com/sites/default/files/images/9jpg_0 (click to expand).
I can easily see why two dinosaurs locked in a deadly struggle might not be completely aware of their surroundings.
It is also possible that they both died during a fight, and thus would have had difficulty running away

And you are certainly not alone in mistakenly ascribing human-like intelligence to dinosaurs, but to be honest I'm not sure what running away would have accomplished in that situation.
In any case--such fossils are, as I said, extremely rare. Very useful, but very rare. And definitely--given the time periods involved--not evidence of any sort of alien activity.