Just an idea...as I see that PHP can check if files exists, tell that it's (if it's the case) impossible to delete a file...

Why don't we ( I know saying we is a bit exaggerated:-) ) include in any of the modules a routine to check a least that the files have been put in the right directories. A kind of Bill of material.

I know that's not enough to say that the module is well installed, but if file are missing we're sure that the module won't work so the module can tell the admin that something is missing.

no ?