Currently an <b>#include</b> preprocessor directive pointing to a non-existent file will terminate the game with a message box informing you that:
<i>Include file C:\Users\Deadfast\Documents\Arma 3 Alpha\missions\test.Stratis\defines.hpp not found.</i>
This happens no matter whether the #include is in a config.cpp, description.ext or a script file.
Instead, this should be handled via in in-game error message, similar to the one displayed when you try to execVM or preprocessFile a file that does not exist.