The heat shield on the catalytic converter of my 2005 Honda Civic rusted and was hanging on by one nut, so I decided to rip the bottom part off. Is it necessary to get a replacement or can i go without it?
As long as you don’t park on top of grass or other stuff that likes to catch fire, you’re fine.
You could have gotten an oversized washer (body washer) and a used it to bridge the rusted out holes, but its too late for that now. If you can bend and drill some sheet metal, you could make a new one pretty cheap. It should be replaced.
I remember when the first vehicles rolled out with catalytic converters. They were catching fire quite frequently because most, if not all, were not equipped with heat shields. I would replace the shield as keith has already mentioned.
If you happen to start a national park on fire, they’ll come after you for the cost.
If you still have the part, you can secure it with one or two large worm-drive hose clamps from the local hardware store. If not, you do risk a fire.