Its not like Marvel hasn't tried that before....remember the Clone Saga? How at one time we were supposed to accept that Ben Reilly was the real Peter Parker and that everything that happened post 1973 or somewhere around that time was null and void? The editors quickly listened to fan outcry and switched things back, I'm sure that the same will occur here.
I kind of think otherwise but it is certainly possible.
The Clone Saga came at a time during the 90's when comics were REALLY struggling again. Marvel was still working off their Chapter 11 (or whatever number) bankruptcy and paying off the bank to keep their doors open. I believe that they were so worried about losing money from readers that they turned it around quickly because they absolutely needed the money. Back then, X-Men and Spidey were Marvel's only bread & butter.
Comics are at a level of sales and popularity they've never seen before...especially Marvel. Also consider the movie revenues, licensing their characters out, etc. etc. and consider that a lot of other characters and comic books that WOULD NOT SELL during the 90's (i.e. Captain America, the Avengers, etc.) are selling like hot cakes and enjoying some monster popularity. Marvel can very well afford a big hit to the Spider-man comics and keep trucking, especially when they have the whole Ultimate line, the X-Men comics, Captain America, Mighty Avengers, New Avengers, Hulk, Iron Man, countless mini-series, crossovers, movies, toys, etc. to fall back on.
I'm not liking it any more than the next fan but I know that this "Brand New Day" thing is not going anywhere anytime soon.