Sure, there's not not revenue in ads to cover the massive overhead of a normal newspaper. But I'd be curious what percentage of that overhead is the salaries of the kind of long-form, investigative journalists you're talking about, compared to how much is their outdated production and distribution models (and the facilities those demand), plus the kind of normal business overhead demanded by such large enterprise (accounting, HR, etc).
Reduce a newspaper to ONLY its investigative journalists, 2 or 3 editors and 2 IT staff, one of whom manages the website where the content is published and distributed, downsize to an office big enough to hold the 5 employees who are actually there during the day, outsource accounting and HR, liscense/syndicate the rest of the daily 'news' from the rest of the internet and then look at the numbers.
I don't know whether or not that's realistic b/c I don't have any ideas what those salaries are like nor what the ad revenues are like. But it seems like a reasonable, albeit difficult, business model. Of course, with the exception of the small town local paper, I don't think anybody has ever accused the newspaper market of being anything but tough. It's on a lot smaller scale than the newspapers we see now (which means profits will be smaller), but I'm hard pressed to see how that's my problem (particularly if your other choice is to fold altogether).
I think there's a place for investigative journalism, and I think it's short-sighted to say that just b/c national newspapers are folding that it'll disappear. It's valuable--the people that want to see it just need to imagine a new way to support it.