aakk9999 - 8:33 pm on Jun 24, 2013 (gmt 0)
I would 301 to the home page.
This is not a good idea - Google treats this as a soft 404.
You could redirect to a relevant page, but if there are no external links, I would have either leave them 404, or better, return 410 gone - they will drop out of index sooner.
"Returning a code other than 404 or 410 for a non-existent page (or redirecting users to another page, such as the homepage, instead of returning a 404) can be problematic." [support.google.com...]