When to close a bug tagged 'will not fix'?

[James Stark <jstark@ieee.org>]

Hello Mentors,

I have a bug that I have tagged "will not fix" and I CC'ed the original 
submitter with the explanation of why it won't be fixed, however the CC 
to the original submitter bounced, with a message saying that the user 
does not exist.

It's my understanding that Debian prefers that the submitter close off a 
bug after it is marked will not fix, but in this case I doubt that the 
submitter will ever find out that the status on the bug has changed.  So 
my question is:  Given this situation should I, as the maintainer, be 
closing this bug? and how long should I wait before doing so?

Thanks,

James