Gizmo_Duck
blathering blatherskite!
I don't think it's that big of an issue because most people are online anyways, but it would suck if you have spotty internet. However, you have to question what happens 5+ years from now if they were to close servers. I think for game preservation this is a bad move because I don't think it's right to lose access to a single player game if you've paid for it.
Also, just for reference, Dishonored is already 12 years old.