So McDonalds, Taco Bell, Dunkin Donuts, Joe's Pizza, and 711 get to stay open yay

It's not about asking "which half". It's that the numbers cannot be compared. If 90% percent of restaurants stay open forever, 60% of new restaurants could close in their 1st year but only 6% of existing restaurants would close. If we say 50% of existing restaurants will close due to covid, comparing that to 60% makes no sense, it needs to be compared to 6%.

You are right that the 60% of restaurants that will fail are likely the ones that were on the edge anyway, however, this is a different distinction.

I think the more important distinction is that this is 60% of ALL restaurants, not 60% of the 10% of new restaurants (or 6% of restaurants).

(I made up the 10%, but I'm sure it is small.)

observationally, this doesn't seem to be the case. In NYC, the way it looks is that restaurants that were doing a brisk delivery business before the pandemic are still with us and a lot of great restaurants that were packed with in-person diners are gone. There are tons of exceptions. Source: Brooklyn.