how can Soft tissue from a dinosaur still exist?

Question

soft tissue impressions in a fossil dinosaur was discovered in Petraroia, Italy. The discovery was reported in 1998, and described the specimen of a small, very young coelurosaur, Scipionyx samniticus. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur.

http://en.wikipedia.org/wiki/Dinosaurs#Soft_tissue_in_dinosaur_fossils

Answer 1

Actually, remarkable preservation of soft tissue can and does exist, even down to the sub-cellular level in some instances. Check out Dr. Mary Schweitzer's work on a T. Rex femur from Montana...she found the presence of spongy tissues with what appears to be red blood cells still preserved.
Other instances include undigested muscle fibers preserved from a Tyrannosaurid coprolite (fossilized feces), and preserved gut contents from Varicchio's work.
The most common form of soft tissue preservation occurs when the tissue falls into an anoxic environment, is swamped with bacteria, and then is quickly buried and mineral ions in the water replace the bacteria, preserving remarkable three dimensional representations of the fossil record.

Answer 2

Soft tissue can fossilise under rare circumstances. The soft tissue no longer exists, it can't, but the impressions of the soft tisue remain.

You can read an excellent paper on Schweizer's discovery and what it means here:
http://www.talkorigins.org/faqs/dinosaur/flesh.html

Answer 3

I think you answered your own question. The soft tissue itself does not still exist, but an impression of it does. Several homonid skulls show impressions of the brain. I'm sure there are numerous other examples.