IMO, the most likely outcome is: initially, they'll stay grounded until the flight recorders from the latest crash are analyzed, and it's confirmed that it's pr

IMO, the most likely outcome is: initially, they'll stay grounded until the flight recorders from the latest crash are analyzed, and it's confirmed that it's probably the same or a related cause (if the cause was unrelated, they might be allowed to resume flying earlier). Then a fix to the software will be developed, taking into account the preliminary results of the investigation; Boeing has a head start here, since they started developing the fix after the previous crash. After it's validated that the fixed software would have prevented both accidents, the authorities will change the rule from "all planes of this type are grounded" to "all planes of this type are grounded, unless they have software version at least X.YY on that subsystem, or are flying with no passengers to a maintenance facility to install that software version". And then the companies which own these planes will install the fixed software, and normal flying will resume.