Debris field size and extent
I suggest a look at the TWA 800 (B747 fuel tank explosion) report. Not because I suggest there is any similarity (there is yet no way for us to tell), but because it mentions (for the time) advanced software modeling to simulate the distribution of fragment trajectories based on their aerodynamic properties (size, weight, "lift/drag") to get an idea of the altitude at which parts separated and broke up.
With far more advanced computers and more accurate modeling these days, such an analysis of the debris distribution (taking into account known winds and currents) will be carried out and will, at the end of the day (... week, month, year, ...) give a very good idea of where and in what fashion the aircraft disintegrated.
Initial distribution of the bigger pieces will give a rough idea early on, whether it was an in-flight breakup, of destruction on impact.
Only time and meticulous investigation will tell.
As to the recorders: I can't believe the authorities have given up on recovering them. This is such a grave and rare event that it is essential to find out as accurately as possible what happened. Every effort will be made to recover those recorders, and perhaps even large parts of the airframe, depending on the findings from the recorder.
Bernd