Scott Karp in Publishing 2.0 asks what would happen to those print advertising dollars if the paper just went online.
He suggests newspaper companies assume all of it would disappear and that they ought to be thinking about how to retain some of it if they end up ceasing publication of a print edition. In short, they need to think through how many of those dollars they could lay claim to in the event of an online edition only.
A few points: I don't think anyone assumes all revenue would disappear, I do think news organizations have calculated what the remaining revenue would sustain, and that's why they continue to produce newspapers and think they'll do so for a long time to come. The alternatives don't offer economic salvage.