It's difficult to say, given the nature of politics (and politicians). It seems that any gaffe, no matter how bad, can be forgiven, overlooked, or ignored if it's in the interest of the party to do so.
However, Hillary may have just stepped over the line by referring to the death of an iconic figure--and then had the added bad luck of the news of the only surviving Kennedy brother's apparently fatal brain tumor to become public.
John Gotti might have been "The Teflon Don," but I'm not certain that Hillary has the same coating--and her remark just might have been the death knell to her aspirations, at least for 2008.