With all due respect, you're both wrong. Gus had nothing to do with Mike being killed (second hand, or otherwise), unless you wanna count employing him in the first place as the beginning of his downfall. No, Mike is the one who got Mike killed, but not because of Lydia. Walt killing Mike had nothing to do with names (he realizes he could have gotten them from Lydia after he already shot Mike), and nothing to do with expansion of business (at the time he killed Mike, he hadn't spoken to Lydia yet about expanding).
You were right about half measures,t hough, CB. How many times did Mike put a gun to Walt's head and NOT pull the trigger? Like, a lot, right? If Mike would've killed Walt in Gus' lab, or in the desert after Gus died or back at the pest control place after Walt hid the methlamine, Mike would still be alive right now. Grant it, he might be in police custody, but he'd still be alive.