Thanks for the feedback on what I should do!  I 
really appreciate the responses.  If I did decide 
to sell it w/o the sketch I would _certainly_ 
tell the buyer it is not included and keep their 
email in case I did eventually part with it.  I 
like the idea of copying the piece... ^_^ In the 
end I will most likely sell the two together b/c 
it's the way I would want it.
Thanks again!

--kouryuu