When you smash a package, the following happens:
After the package is smashed, the symbols continue to exist, but all the information they contained is gone. By being uninterned they become eligible for garbage collection. Also, the chances of any objects they referred to being collected are increased.
CAUTION: Smashing destroys a whole package and all information within its symbols. Use it carefully.
Note: Any symbol whose home package is to be smashed can be retained by being uninterned before delivery commences.
LispWorks Delivery User Guide - 13 Dec 2011