New Gaskets Or Not?

I would replace them, don’t cost much and will save the hassle of possibly having to strip it all down again.

 

I would agree and replace them also. After all, you'll never have a better time to do it!

 

I suppose if they stay in place you will get away with it. If they fall out you will need to replace

 

Also be aware on exhausts really it is best practice to retighten any manifold bolts/nuts after a couple of heat cycles have settled things down.

 

Just that if they are fully crushed and not compressed parallel, there is more likely to be a leak than if they mate up exactly
as they were originally . I suppose it depends how much they were tightened initially

 

Not just tightened but more importantly how true the alignment was. Engineering tolerances sometimes cancel each other but not often.