So the answer is twofold. First the cost of cases themselves and then how people react to them. But you're looking for an objective metric when there isn't one.
Here's a simple example: How are you going to go out for a meal at a pub when you need to wear a mask the whole time? That's not an objective metric, but people are not going to head out to bars etc when every 2nd person is likely to kill them with an infection unless they have a mask on.
I can't be objective about the cost to business of every infection - an employee being off work for a month, a director being off work for a month, an employee dying, a director dying, so on and so forth, and yet I guarantee you these things will happen and will cost everyone a boatload. Same as with zoom meetings etc being such an effective alternative, people simply aren't going to travel for business or really do much at all (even go to the hospital) unless they ABSOLUTELY have to. This isn't modelling, this is behavioural economics - not objective by its very nature.
Sure things will pick up for the next couple of weeks, but the moment serious infection numbers hit the news (which they are going to) is the moment EVERYTHING changes. We know this because they already did the second the last ones did. You're essentially claiming this pattern of response to the virus data is not going to be repeated.
I also can't give you an objective metric of X number of cases where states and municipal areas reclose or just flatly never reopen particular areas, but I bet you it still happens, same as I bet you people aren't going to go elbow to elbow in bars when the infection rate is 500x what it was in feb. People weren't taking the virus seriously before not least of all because of the low statistical probability of actually getting it. That's going to change, and change dramatically.
People are now very wisely avoiding (only) the hospitals because they're infection hotspots. What happens when the whole country becomes a hotspot, which it will?
Again, this is what numbers *can't* show, but it doesn't mean they aren't true and/or won't happen.
We see a drop in whatever economic activity has just been restricted and a commensurate drop in the market in response. Exactly like what has already happened?
Seems like a bit of a silly question to ask what'll happen to the market if economic activity is re-restricted?
Sure it does - it means you won't see the bump as high as you were anticipating. If enough don't reopen or some more bad virus data is released, you mightn't see a bump at all. Either way, the outcome (in the short term) is not as positive as it would have been.
Sure, and I'm doing the same thing - you're just trying to use modelling to do it whereas I'm doing the complete opposite. You seem to think there's nothing that your models can't tell you though?