We have an answer, courtesy of Steve Wasserman, Hitchens’ literary agent:
“In accordance with Christopher’s wishes, his body was donated to medical research. Memorial gatherings will occur next year.”
I wouldn’t have expected anything less.
Please consider donating your body (and organs) after you die — there’s no better way to “live on” than helping people learn and live even after your own passing. Each state has different rules/requirements, but a couple starting points are here and here.