"Hello Charles. So you didn't make it." Wesley sounds resigned rather than horrified. Detached, really. As though death is just another damn thing that's come along and he's observing the aftermath from a long way away.
Gunn doesn't feel that way. Not yet. He wanted to live. Still does want, but looking at his intestines spread over the alley, under the feet of the rampaging army of evil, he has to admit it doesn’t look too good. His view of the battle is fading fast, as he slips his hold on mortal life. But it doesn't seem unimportant. He wants to know the others live.
Right on cue, Wesley says, "I fear the others will be following us soon."
That gets Gunn in his clawed-out, trodden-on, completely illusory gut, so he can't help but babble. "No. No way. They have to live. Gotta live. It has to mean something. All of this futile fight… There has to be something that comes after. She has to live."
Call it post-mortem stress disorder, because that was just careless talk. Gives Wes an opening. She won't live, Charles. She died long ago, because of you. So burned up and spilled to the winds that there's not even a spirit Fred to join us here waiting for the rest of our dead to join us.
But Wesley doesn't say that. He says, "It already means something. It means we gave it our best shot. For her."
He pauses, and Gunn notices that the world has continued to fade while they talked. He's very nearly gone from life now. But Wesley's holding out his hand, his supposedly illusory hand which now feels very real as Gunn grasps it. He doesn't have to say words like 'scared' or 'what comes next?', let alone 'heaven' or 'hell'. Wes is in the same spot. Wes understands the fear of the unknown; the fear of going on alone.
"I think she knows that we tried. I think that matters," says Wesley, as they step together into the unknown future.
Finally, Gunn believes he's forgiven.