I read an interesting article on Inc Magazine about handling people that leaves our company. I think the writer has a good point, it is better to have a good break up and leave a positive feeling on both sides, you may end up doing business together in the future.http://www.inc.com/articles/201111/how-to-break-up-with-employees-.html
ofc - what is the potential good in not keeping a good relation?!?! People have a need to develop and grow, if they cannot fo that within your company, then you should try and find out what is missing and fix that whilst wishing them a good continued carrier elsewhere. Trying to keep someone that is obviously wanting to leave is hardly a good long term solution as dedication etc is likely not peaking.
SvaraRadera//Marcus