I wish the best ending would only be achieved if Mike has been kept alive.
Picture this:
This is the end. You're fighting the big alien momma boss, and you're losing. The only way to win would be to switch on the nuclear bomb you've succeeded in placing in her nest where she's drawing her necessary lifeforce. She's been exerting mind-control on the crew and you're too weak to fight it anymore. Mind-controlled Kelly shot you. Annie and Sarah, now the creature's puppets, lie motionless on the ground, and you can only pray they're just knocked out.
You're tired, you haven't slept in days. Home feels a lifetime away. The creature smirks at you, approaches slowly. It can feel what you feel. It revels in your hopelessness. One step. Two steps. It's near, you can feel its fetid breath on your face. You're so tired. Time to sleep now...
When suddenly appears Mike! All bloody and crawling to the bomb switch. He knows that he won't survive the blast, but he does it nonetheless: "I! Do! This! Every! Day!"
Cue epilogue.
Goodnight Sweet Prince and flights of Ophions sing thee to thy rest! (T-T)7