would explosive decompression have broken the cockpit away?
Decompression on a craft perforated by a few hundred fist-sized holes? certainly.
The cockpit and the tail section ended quite far apart, in clean condition. If the missile exploded low enough, some shrapnel could have hit the fuselage where it narrows, helping to detach the rear section. Cockpit and port wing show a lot of missile damage; the tail I can't see yet.
A lot of the main fuselage is missing/smashed/incinerated, to the extent that the OCSE (political) observers are claiming the "rebels took the fuselage away" . There still exist small sections of fuselage, one piece of overhead lockers that I've seen, a big curled section standing on end....
The port wing seems to have taken much of the initial blast, and broke off, unburned. Starboard wing and engine seem to have stayed attached, ended up burning. Fire started only on impact when the centre fuel tanks ruptured. The port wing by this time too far away to flash over to that. Cockpit would have separated early on, or just held on by a thread until ground impact, which was most likely not nose first.
Fuselage+right wing unit would have tumbled, raining out people and cargo on both ends; most would not have burned, the ones who did will be hard to recognise. Most would not be strapped in (mid afternoon and awake) and seats were dislodged from the floor (or the floor from the frame) by the missile impact, though some appear to have concertinaed on ground impact (some empty).
They were not "drained of blood" as that silly rebel said. But they would not have bled a lot, perhaps that's what he meant. By the time they got whatever hitting the ground injuries they got, they were indeed dead, combinaton of freezing and no oxygen up there. Horrible as this is, at least they'd not have known what hit them, literally, unconscious while still in the first surprise stage of what's happening??.