If i understand you correctly, you simply remove the call to glewInit and the linker-setting to link to glew.
If you don’t do anything else, that simply means, that your extension-pointers won’t be initialized AT ALL. There is no default fallback that kicks in. You would need to do everything yourself (or through another library such as glee).
If you include glext.h you get at least some enums defined, which you might be able to use, but you don’t get any function pointers initialized. So basically, if your app still tries to access any of those functions, you should get a null-pointer exception.
So, how much your app gets “broken” by removing glew depends on how much it tries to use extensions, but in most cases you will get into trouble fast. What i really meant is, that by that move you really remove functionality, you don’t get it replaced automatically, so if you were not aware of that, you basically introduced a “bug” that might bite you later on (but now you know ).
On Linux this might be less bad than on Windows, afaik on Linux you get much higher OpenGL versions by default, on Windows the default OpenGL version is 1.2 or 1.4, so using glew is essential there. On Linux i am not up to date what you get by default.