Well Mirror's Edge has been out how long, a couple of weeks? According to some website I found the average video game released on both consoles only sells 408,336 units. If ME is already 3/4s of the way to the average after only a week or two, odds are it will probably exceed that average with the xmas season coming up. The same report, says only 20% of video games are profitable. http://blog.mlive.com/manzero/2008/11/only_20_of_games_make_profit_s.html
Of course, it all depends on the game's budget a well, which unlike movies is probably not something that is readily available. I've also seen on other websites that it may have had some competition released against big titles like Gears2, Resistance2 etcetera. Games which may already have followings as opposed to a new game which does not despite whatever hype it may have.
So who knows. The customers will have their say and then the tie-bound pencil pushers can decide on the game's future.
EDIT - that same website also says that 25,000 units sold is equal to about 1million in revenue. So with 300k sold it's made what, 12 million dollars? I'm not sure what the average video game budget is these days. . . .