It felt contrived; a deliberate effort to show that Gears is more than just Guns n' Guts, but it really didn't make much sense to make a potential suicide mission detour considering the millions if not tens of millions of people that undoubtedly died on Serra during the Locust attack.
Yeah, he lost his wife; it was terrible. Lots of terrible things happen throughout the story to just about everyone in the game. If it had been any other character, Dom's obessive to the point of neglecting his duty quest to find his wife, who in all probability was dead based on the sheer number of casualties, would have resulted in his death. I thought it was actually a pretty irritating sub-plot.