They are two separate things. Brexit weakens the EU, and makes its collapse slightly more likely but the real threats to the EU are not related to Brexit and whether it lasts or not won't be related to the UK, we were never involved enough for that to happen.
it weakens it to the point where tarrifs and exporting to us make it harder......but the pain is split
france export 10% of their exports to us....germany 8-9%.
the rest less.
we export 44-47% of our exports to the eu.
investment will fall here...some companies will move tot he eu based on trade within the eu.
way i see it is we are hurt more than the eu....a lot more.
they may lose a fraction on tarrifs but they will gain some back on investment.
they are also not at a high point where as we are....they are slowly and sensibly coming out of the crisis.
we dipped our toes in but never suffered anywhere near as much as some of the eu did.
there is way more downside to our fall than theirs.