There was an episode where Justin tells the maker of StarSan (Charlie Talley) that he racked a 5 gallon batch onto something like a gallon of starsan, realized it happened, and then dumped the batch. Charlie basically told him that the beer should have turned out just fine. The constituent of StarSan would break down to fairly normal ions and actually feed the yeast. That might not have directly applied to finished beer but under a quart and I bet you won't even notice. It is food grade, no rinse, and a weaker acid than you find in your stomach at the recommended concentrations; you are diluting it massively with something like a 4.5 pH beer so you won't even really acidify your batch much. I say drink it. Then, if you aren't convinced that the impact was nothing to worry about, try this: take a glass of another batch and compare to another glass of the same beer but with a similar starsan concentration added (just less than an ounce added to a pint by my rough math). Then, take another pint and add the same amount of tap water. I am willing to bet, if you make the starsan with RO or DI water, you notice the minerals in the tap water before the starsan beer.