Nowhere, most likely.

People need to face the fact high speed internet, the new ways to consume TV (even the legal ones from DVD to Hulu and i-tune), and the multiplication of the availability of media in which to advertise have fragilized the business model a lot (at least in the US where it's all private. 90% of TV outside the US are in some way and extent subsidized - the price to pay to get a local product on the air), while at the same time the audience are more and more demanding in terms of production value (at least for fiction.. and it explains the joy of the networks when reality TV really works). If the space is available and the budget allows it, a network might move an established show that lost speed to a less performance demanding time slot expecting enough of its audience will follow it there for it to meet expected ratings in that slot, but they can longer afford to keep a show not performing as the advertisers expects in one of the lucrative time slots for very long, especially not in the slots where the 25-40 demographics watch TV (as it's them the advertisers want, they don't care nearly as much for teens and elders - agencies even screen them out from the ratings) Years ago, it could be construed as greedy, in the sense that it was often a matter that the broadcaster thought it could generate even more profits from a time slot, but nowadays it's much closer to a matter of survival: they need badly those revenues to keep going, and with any lack of performance the advertisers are keen to look for alternatives. There's also the fact that at some point the broadcasters saw the home market as new extra money, but nowadays they see it as necessary revenues. A show that don't perform most of the time won't sell well afterward either. The price American shows fetch abroad has also gone down, as foreign broadcasters face the same challenges regarding advertising but are keener to cut down costs, and the offer has multiplied a lot (eg: any show the BBC, Fox, HBO sell to a broadcaster - and there's more and more of those available - are time slots they won't look for an ABC, NBC, CBS etc. show to fill). A show have to work really well in the US nowadays if it hopes to fetch a good price abroad (and even then... in Québec most of the US shows on the air are now on cable stations that won't pay anywhere as much for them as our big networks used to pay for shows like Dallas, Dynasty and so on back in the day. The big public network picked Lost and Desperate Housewives in recent years, and that was for its summer grid...) .

Eventually the situation might stabilize when the networks solve the problems related to financing, but it doesn't look to be for tomorrow (apparently Hulu still generates around 100 millions $/year in advertising, and that's a drop in the ocean compared to the broadcast advertising revenues or rather their decline. A paying model isn't all that attractive considering it will have to remain cheap enough not to lose Hulu users to piracy).

In the meantime the choice is pretty much between seing shows pulled off the air abruptly or getting production costs back down to a more comfortable and manageable level (which the networks find far more high risk). It might get worse - the bad economy is good for TV. People watch more TV, and the announcers have higher budgets during an economical crisis than they do when their sales are going well.

As for Fringe they could very well cancel it, but I guess that giving it a season or half season to wrap up could be more likely, unless they've already asked its creators to wrap it up for the end of season 4... unless it's losing them too much money, or they need its slot for a show they hope will perform really better. There's not nearly as much to gain from pulling the plug on an unfinished series like Fringe after 4 seasons without giving it an ending as there is pulling a new series off the air. Pulling the plug on Fringe now means the DVD sales will become marginal, it will be difficult to sell it to any new buyer as the series is unfinished, and they'd lose the present revenues from foreign sales (typically, series like Fringe abroad are grid fillers, so buyers usually purchase them to the end of the series. It's more demanding for Fox to sell a new show to its foreign buyers than to renew a deal for one more season of Fringe...). That played in the decision to finish a show like Alias (not Fox, I know) despite its decline for instance.