Decompression, hypoxia: it seems most credible scenario. Too early to say, true, but 8 minutes of descending without any radio communication would confirm some degree of incapacitation.
We have seen it before. If we then combine the hypoxia theory with the very busy military area just 25 miles before crash site, "friendly fire" is not an entirely an impossible theory. Damaged fuselage, decompression, hypoxia.