Well, I can tell you that from a reenactment I've seen, Westminster Hall would have been entirely destroyed, killing James, most of the Lords (including several powerful catholics), most of the Bishops, the 2 Archbishops, lots of wealthy merchants, the MPs of the Commons and probably some people outside due to chimneys collapsing etc.
Afterwards, the plan was a Catholic regency for Princess Henrietta. Very unlikely to work as the moderate Catholics (not being overly persecuted thanks to Elizabeth) would view themselves as loyal to the King above the plotters, so they'd have very little support. Probably more Catholic emmigration to the Americas, less Puritans go. Perhaps the initial demograpics of Massachussetts and Maryland end up swapped.