I wasn't really clear before but long before Dragon Commander was announced I assumed the two games was that one continued the DK's story and the other the divine's and somehow the storylines of both games came together. Now as more info has been released this obviously isn't the case. From what I can gather now Project E is the 'sequel' and Dragon Commander is a sort of spin off.
I was just wondering if DC was set in the future or past the latter seeming more likley now. As for your character being killed off if they did choose to do that what you said about us seeing the DK's being killed off one by one (prehaps the ending cutscene) seems to make more sense. However if they chose not kill the DC off well it's got me thinking... I suppose the game will simply end when you have conqured everything.
As for lifespans I thought it was just true dragons such as the Patriarch that lived for thousands of years. The DK's longer than a human but not that long.