Trouble/questions, replacing exhast????

98 Honda Civic EX manual with 78,000 miles.
pipe broke just before the exhast. I just removed from the cat back,
including the cat.
Looks like original exhast.
(I have the front end on ramps and the rear is on jack stands so access
makes it difficult to get stubborn nuts off so I usually end up cutting them
off.)

I have to decide what to replace?

1. - Muffler?
The muffler says Honda on it. It seems to still be in good shape. it does
rattle when shook, Something, rust?, inside...
How wuch longer might it last?

2. - Pipe between the muffler and Cat.
This pipe broke right behind the flange that attaches to the muffler. this
has to be replaced. This pipe has a resonator and the front end attaches to
the catalytic converter.

3. - Catalytic converter?
I had to remove a heat sheald from around the cat. to get at the 3 bolts to
seperate the bad pipe from the cat..
I couldnt get the rusted nuts off this connection so I cut the ends of the
bolts off with a dremil.
A few smacks on this connection with a hammer and I was able to get the pipe
out from under the car.
PROBLEM! - I have to get the rest of the bolts I cut, out of the flange on
the cat. They dont have a nut on the end. It looks like they would be T
bolts from what I can make of the rusted ends. I tried banging them out with
a hammer but they dont budge. I'm afraid the are not bolts but part of the
flange on the cat???? If this is the case can I cut/drill them out and reuse
the cat. with bolts to hold them together???
OR should I replace the cat now while I have it all apart????
I disconnected the O2sensor and removed the cat so I could work on getting
these 3 bolts out..

Do I have to replace the gasket at the front of the cat? Its still attached
to the manifold pipe on the car. It looks in good condition??? I replaced
one before that had deteriorated to almost nothing... Or do you always
replace these gaskets?? (flexable joint with springs and bolts..)

Also, should I replace the O2 ? Can they be tested? I know they are
expensive I just eplaced one on another car.

Trying to save money doing this myself but I'm not sure reusing the old
parts is cost effective????

Thanks For any advice..

Steve