Miller, currently, has negative value. He has not played well for a long time. Buffalo should be trying to basically give him away to free up cap-space.
You clearly haven't watched this team. Miller has made spectacular saves and been a bright spot in pretty much every game we've played. Our defense (not just the d-men, but the whole team, including backchecking forwards) has been absolutely atrocious. That he even has a sv% over .900 is amazing to me. This team is letting him down night after night, and he keeps doing everything he can to bail them out.