Will driving with a bad catalytic converter cause the EGR valve to go out?

The catalytic converter on my wife's 2007 Town & Country went out, but it is still under warranty. The service advisor at the local Chrysler dealership says they are on "national back-order"; they don't know when they'll be getting any in. In the meantime, the van is running horribly and sucking a lot of gas because the EGR valve (which is NOT under warranty) is also out. The service advisor recommended that I go ahead and replace it, he says it's a coincidence that they both went out at the same time and that driving the van with a bad catalytic converter won't damage the EGR valve. But another mechanic, who's not affiliated with Chrysler, tells me that driving with the bad catalytic converter is probably what caused the EGR valve to go out in the first place and that I shouldn't change it until the catalytic converter is replaced. Should I go ahead and replace the EGR valve or not? It's going to cost over $300, so I don't want to replace it yet if I may wind up having to replace it again.