Hi, Why not do all three; header, robot.txt, site map.
Of course safest would be to delete the pages, but only if the pages are to no use for the visitors or they can,t find them, I suggest you delete them.
If you do, then use "mod_alias" or maybe "mod_rewrite" to tell they are "gone" (410). - Ask in the Apache Configuration forum how to redirect visitors to a 410 page.
PS / This is a SP post card.
EDIT) This was apparently not a recently opened browser tab by me. 8.33 GMT I see it was.