There is a also the oncleanup callback that can be executed whenever your function ends, regardless of the reason.
There is no way to prevent the user from stopping your code and there shouldn't be.
I would strongly advise you to rethink your strategy though. The less user friendly your code is, the less inclined the user will be to use it. If you catch error messages it should be to better explain what went wrong, not to hide it.
I also worry that a) you want to prevent errors being display, indicating that your code may not always work as it should and b) prevent the user to stop your code if it goes wrong. What if your code goes into an infinite loop?
You've encrypted your code, so the user cannot look at the source code anyway. You should leave at that. Or if you do catch errors / invoke cleanup functions, it should be for the right reasons: make your code more robust.
