Q.peppers
I know that red pepper plants die after a freeze, but are the peppers that have already ripened on the plat still good? I will be using them to make pepper sauce with vinegar.

Certified GKH Gardening Expert
As long as they are not brown, they are fine to use. Sauce would be perfect because they get a bit soft after a freeze.

I think that you are saying that your pepper plants have been killed by the cold/frost while there were peppers on the plant. I'll go off that assumption:
I would think that any vegetable or other edible would be fine as long as it hasn't softened too much or started to deteriorate with black spots or mushy spots. If the peppers seem intact, it seems reasonable that they would be fine. If they are still on the plant, I would put them in the refrig right away.
It sounds like you will be cooking the peppers to break them down then add your other ingredients to make them a sauce. I would think that, if there were to be a problem with them (which I don't think there are), the slow heat and the vinegar would help to kill any bacteria.
Hard to answer this question since I can't see them and don't really know the condition of the peppers. Good Luck to You!