"There'd be a certain poetic justice to it, yeah," he agrees dryly, watching Spike, because he can see behind the banter that there's a real desire to just die there. It's not something he's prepared to give, even temporarily.
He follows Spike's glance down to his wrist and then looks back up at him, smiling faintly. "I'm not going to stake you, Spike," he says gently, very close now, intense blue eyes on intense blue eyes. "But I will give you this."
And he cups the back of Spike's skull with one large hand and pulls him in for a kiss. Gently enough that Spike can easily pull back if he wants to, but firmly enough to demonstrate that he wants it, and at least as much to comfort and distract as because he's always had the hots for Spike.
Even if Spike does pull away, or head-butt him or whatever, he'll still count it a victory in getting him to actually feel something again.