An “extremely distraught” Steven DiSarro, dubious about a sit-down he’d been summoned to with the godfather of the New England Mafia, left a note at his home in Westwood for one of his sons telling him it would be a while before they saw each other again.The nightclub owner then stepped into a waiting ride and vanished, prosecutors plan to tell a jury later as Francis “Cadillac Frank” Salemme’s murder trial gets underway this month.