I suspect I am misunderstanding your question in at least a couple of different ways. Could you clarify?

I think I already believe that there's no right and wrong, and my response is to largely continue pretending that there is because it makes things easier (alternatively, I've chosen to live my life by a certain set standards, which happen to coincide with at least some versions of what others call morality --- I just don't call them "moral"). But the fact that you seem to equate proving the absence of morality with proving all utilities are zero suggests we mean different things by the words; they strike me as entirely distinct propositions. I'm also having serious difficulty imagining a situation where I still have wants and desires (maybe even values), but there's no utility. Help?