I've seen this happen once, I suspect this is a general bug but haven't played enough to be sure.
In my last full game, Vetrar (sp?) went pretty far outside of his wildland and stayed outside. I killed him outside, and cleared everything in the wildland but the wildland never cleared. I did get the items (fist of Vetrar? Sword of the Glacier - or something like that).
Now I'm playing another long game on a huge map, and I see Delin wandering far outside of his wildland. I'm hoping he wanders back in, but based on past experience that's not a good bet.
Has anyone else seen this bug? Is there a workaround? I'm wondering if there's something that triggers the wandering (like maybe if Delin spotted my scout and that's what triggered his wandering - if that's the case, maybe I could have scouts steer clear of wildlands until I'm ready to kill). Or I'm wondering if it's possible to lure Delin back in?
Or maybe the wandering of bosses is common, but whatever happened w/ Vetrar was the anomaly? (sounds to good to be true)
Boy, I'm sure wishing I could go back to 1.4, 1.5 has seriously made this a worse game.