To expand upon the earlier answer by Radiance.
When you execute a file within a zip, Windows does a temporary relocation first (of that file only), before executing it. So in that scenario, all other dependencies (other files/folders) will not be relocated, so a simple FileExists test will be your solution.
Good coding practice, includes using FileExists at all points anyway. Never take a file or folder existence for granted. Be judicious though, as once code is running, you only need to test once during the life of the running script ... unless you cause something that makes a file location or existence (etc) change.