If they knew in advance, at least capture York (who just sleeps almost all day) so she can't do more harm, reprogram ALL pacifistas and Seraphims' authority chips so they don't answer to people you don't want it to, and send the broadcast while you're alive so you can protect its integrity.
Why would Vegapunk choose to keep all the researchers and Sentomarou on the island if he knows they're all going to be slaughtered? Why would he think letting himself get killed is the better option? There's so many questions here, this arc is completely screwed.