So the resolution of this bet will be simple: on May 11 we will check the (AP) reported delegate counts and do Hillary - Sanders. At the moment of writing this it is: 1705 - 1415 = 290.
On May 11. most likely results of West V. will be included. There might be other states (I have not checked) where not yet all delegates are reported. If they would be reported by May 11 we would add them as well.
This sentence "rom the start of market to resolution there will be primaries in NY, CT, DE, MD, PA, RI, IN, Guam, and WV for a total of 894 delegates." was only for giving context - we will resolve the market according to this: "What will the difference in delegates be between Hillary Clinton and Bernie Sanders on May 11, 2016? This is calculated by (Clinton delegates) - (Sanders delegates) and excludes superdelegates"