I went to a shop for an estimate on my rattling exhaust and I was told that my catalytic converter has gone bad and that is what is rattling. I was just wondering how urgent of a repair this is as far as keeping the car running goes, and also if there is any danger of something coming loose and falling off...

And the year and engine are??

My bad, 95' Monte Carlo Z34 3.4 liter

My bad, 95' Monte Carlo Z34 3.4 liter
This can cause a blockage as the inner shell is broken away, other than that it is harmless.

the affects will more likely be exhaust restiction and if the cant exhaust it cant run

How likely is it to get to the point the car cannot exhaust and therefore cannot even run? At this point, with all the issues this car has, I am thinking more along the lines of just getting it through like 1 last 10k mile session.