you can get a new cup & jounce from the junkyard, ZJ fronts will fit the TJ front and rear. Also crown automotive sells new jounce bumpers.
the tower is threaded, so if you somehow cut the cup off without disturbing the tower, you're still left with a bolt threaded into the tower. that you can't get off.
my suggestion is take a wire wheel on a dremel, shove that up in the cup and clean as much rust off as you can. then take a new grade 8 nut, a big one, say something that uses a 3/4" socket, and super glue it to the rusted bolt. Then turn your welder up hot and weld that nut to the rusted bolt from the inside of the nut. Wait till it cools, then grab on to the bolt with your socket and see if you can twist it out. You'll want spray PB Blaster directly into the top of the tower so make sure the bolt is plenty soaked before starting.
worst case scenario, you have to cut the tower off and build a new one out of pipe.