The Draconians, as they existed, are extinct, save for a few individuals from what I know. From their DNA, the Collective created an altered version of them. Through he methods the Collective uses to control them, they are not the same mentally as the original draconians. They have the bodies of the Draconians, but their memories and thus personality are fabricated by the Collective

As for how they were destroyed, two of the Nations from the milky way already controlled parts of other galaxies, The Draconian home galaxy had been completely obliterated by an unknown alien species and the Draconians themselves were spread thin fighting off other aggressors etc.

As for a summary
http://starempiresreboot.wikia.com/wiki/Triarian_Collective

A lot of reading.

Oh, some of that might be outdated, I do need to go through it and sort some of it out

Edit: Would those seeds work on the Triarii worlds? (Tempreture in excess to 400C at the lowest and going up to 700C)
Would the 'warp tracking' work on the Triarian method of jumping between systems, since they exit this universe and travel through another?
Would the foreign particle effect creatures that don't breath? (True Synths under the Collective don't perform respiration)
There are more questions I'll have to ask when I come up with them lol