It probably won’t crash i.e. they will retain enough market share domestically if the EU enacts sufficient protectionist policies.
Export markets will of course collapse outside of the very high-end. But that has been slowly occurring over the last few years anyway.
It was very strange when Germany was one of the countries blocking protectionist policies for car industry. If they keep going for short profit avoiding retaliatory policies, it may get awry.
I think there will be even stronger trend of european brands put on Chinese made cars. Like Renault is already doing with Dacia Spring. Brands themselves will survive, even companies themselves may survive, but many of them may be just headquarters. Moving production means supply chain follows. And that's where most of the jobs are. Over time R&D will follow factories. So for the job market it could be pretty close to full-on crash.
Because they believed the actually had a chance of remaining competitive in the Chinese market.
Turns out that was highly delusional in hindsight.