He could save Atlantis, defeat the Wraith once and for all, find a million ZPMs so Earth would never be without protection and maybe even cure cancer and it still wouldn't be enough. He could destroy the Goa'uld and the Replicators and all those other bad guys he'd never even imagined existed a year ago and it wouldn't change the fact that hundreds, maybe thousands of people are dead because of him. He woke the Wraith, and it's his fault they're coming and no amount of heroics will ever change that.
He doesn't think about it much, not really. Lately, at least, he's been too busy looking for potential Alpha Sites and making plans and trying to keep the members of the expedition team from panicking at the distinct possibility that they're days away from having the life sucked out of them. But that doesn't mean that in those rare moments when he can stop working and close his eyes, he doesn't see Sumner's face in those final moments and think that maybe now he'll understand how he felt. Maybe now he'll know if he imagined that look in the colonel's eyes that meant he would rather die by a bullet than have the life slowly drained from him.
He keeps thinking there will be some last-minute reprieve. There always has been in the past; that's the only reason he's still alive. But the hours and days creep by and nothing works, at least not well enough. Colonel Everett and his men come with new supplies and the promise of a ship and he thinks maybe this is it, but one brilliant plan after another fails until there's only one choice left.
It won't make up for waking the Wraith, or for the people who have died on all the planets they've visited and many they haven't. His death won't bring anyone back. But maybe...maybe this way Atlantis will be safe and Earth will never have to face the Wraith. And whether or not this works, he'll have no more blood on his hands.