There are a number of facts which will affect this: (please note- I am NOT in the industry, just trying to think the issue through logically- which can be dangerous)
1. Shows' loss of income- obviously, the shows are not taking anything in right now. Now, most of the productions/theatre owners/other interest holders likely have some sort of business interruption insurance or event cancellation insurance, but these may have exclusions which render this kind of situation not covered. Also, they certainly have SOME type of maximum amount they will pay. So while insurance may make up some of the lost income, it will not do so indefinitely. How much insurance helps a production depends on what kind of insurance was purchased and how long this lasts.
A lot of the shows WERE (according to grosses analysis on Playbill) selling at or near (or even above) 100% capacity- so there COULD be room for at least some reserves. (I do realize this capacity was sometimes obtained via deep discounts on tickets) Do productions put aside "rainy day funds"?
2 Expenses- While not bringing in income, the productions' expenses have to be substantially reduced. Do they still need to pay rent to the theatre owners? Even if they do, might a theatre owner prefer to have a show set up in their theatre (even if they lose a little rent) than face the re-opening with the theatre dark? How many productions are going to be planning a Broadway run until we know when "the show can go on" again? (This may actually HELP some of the shows stay open- gives reasons for theatre owners to try and work with them).
The other expense issue is the cost of restarting. Promotion may not be a big deal- the reopening of Broadway will likely be in the news. However, there will probably be some costs to get things up and running again. Some level of rehearsals/run throughs will likely be needed, if only to make sure mechanical sets are working and to make sure everyone remembers specific blocking to avoid being injured by standing a foot or so away from their usual mark and end up getting hit by a set. It also may be necessary to bring in some new cast members and get them rehearsed
3. Casts and other professionals/employees - Assuming they aren't being paid, actors, stage hands, musicians, dressers, makeup/hair people, etc may eventually need to look for some other jobs. Its conceivable acting venues elsewhere in the country may open before Broadway and people will go to those. People may need to take non-performing or even non-entertainment jobs. With "work from home" a possibility, there may be jobs to be had. If the new job includes a contractual obligation (or requires moving to a new location), suddenly the production has to hire people- adding to rehearsal and other re-start costs, and possibly slowing the ability of a production to reopen. Yes, I know all these folks have contracts with the productions they were with at the time of the shutdown, but will these be enforced if the folks aren't being paid? Plus if someone's contract runs out with no guarantee of when the show is coming back, they may simply move on.
4. Effect of shutdown on other businesses- Sadly, some restaurants and hotels are not going to survive this. If this becomes too severe, the Times Square area may drift back towards the "bad old days" before all the work was done to bring business in. While less of a direct effect, if hotels/places to eat are limited, its simply not going to be as pleasant for out-of-towners to come to shows- making recovery harder.
OK, so I've probably overthought this. But my point is there are a number of moving parts here, making it hard to predict what shows will survive. I also think its a bit naive to take the "Broadway will bounce back stronger than ever" view. A number of shows closed after 9/11 and that involved a relatively short closing (yes I know people were scared to travel after that, but the same may be true here in different ways). All we can do it wait and hope.