What happened? Er, all the Time Lords died, just as you said. Is it out on DVD? No, because there were never any episodes made that actually showed the great time war, it was just mentioned in passing a couple of times.
The Great Time War was part of the backstory to the Ninth Doctor.It may be something that will be brought back at some time.I think that it was probably explored as much as it was intended to be as the beckground to the appearance of the Daleks.