This could end up being somewhere between a wash and a net bad thing, also. You are all of a sudden competing with a larger group of people with a large group of miles who will be chasing the same seats you may be.
The airlines have been pretty shameless in recent years about goosing short term revenue by selling miles to third parties (credit cards, etc.). All else being equal, you’d expect the troubled airlines to be worse offenders. Getting rid of Delta and Northwest may help, but United and US Airways (and for that matter Air Canada) have likely been churning out tons of miles in recent years too, given their respecitve parlous conditions of late.