i had to remove part of the heat shield on my toyota corolla S, what will happen if i don't replace it.

In my experience with heat shields it that if the come off, it makes no difference one way or the other. Mechanics at the dealer have said so, and independent shops have told me the same thing. Basically all a heat shield does is take and divert the had from the exhaust and cat from making the ground too hot. While it's a good thing to have, and would never suggest taking one off (it's a benign part anyway) unless you park on top of leaves or an underground C4 storage unit, I wouldn't worry about it. I've had AT least 4 fall off cars I've had, and the only difference I noticed was the sounds of silence. Hope this helps.

Exactly. Pieces of junk designed to fall apart and make the dealers big bucks to replace