Symptoms
After uninstalling the product, there are still artifacts left in the environment. The sites and appPools, SQL DBs and files in "Program Files (x86)" are all still there after K2 has been removed.
Diagnoses
We leave a certain set of "artifacts" in the environment after removing the product. We do this because we do not want to "break" existing functionality.
Resolution
We leave the K2 site and appPools, because you can add "applications" under the K2 site and use the appPools for other applications.
We leave the DBs because you can "move" a K2Server to a different box by uninstalling and re-installing K2 Server elsewhere.
The files left in the "Program Files (x86)" directory should get deleted after a restart. (Only blackearl and smartforms require a restart.)