They'll know in a couple of days what happened since they already have the recorders. With one crash every ~6mo (someone can crunch the numbers and get the naive probability of a crash per flight) and every pilot of a MAX8 now on the lookout for possible problems the public is not seriously put in danger by another week or so of these aircraft flying. Imagine if Boeing grounded these and it turned out the second crash was pilot error. That would be a footnote that would get 10sec in the news months from now. Do you want to be forever known as the guy who tanked Boeing's reputation over a false positive? That has costs to society too. And before you say yes remember that it's much easier to say you'll give your lottery winnings to charity before winning the jackpot.