You wouldn't be able to demonstrate that was only because of diesel emissions from dodgy VW engines.
Individually, no, but a class action (say from emphesema sufferers, or asthmatics) or a government action on behalf of health service providers wouldn't need to demonstrate individual cases, but rather that there is documented evidence that some of the emissions have been associated with health effects.
O.
How could they do that? They'd need to be able to quantify it.
No, they just need to show that the particulates that are being produced in excess of what they originally claimed have been linked with health problems. Once they've done that Volkswagen will settle out of court to avoid having it dragged through the public eye that they are trying to push down the dollar value of the lives they've affected.
Proving the link is easy, and therefore they know they'll lose. They therefore won't go to court - what settlement they come to out of the public eye, of course, will be mitigated by them pleading to the various governments that the hit they take will affect jobs and productivity... and so the greasy wheel keeps on slipping and sliding along
O.