Honestly, I don't know if it matters anymore. I don't read any Spider-Man books aside from SSM, USM, and SG. I could say that killinf MJ would cause me to cancel all the 616 Spidey books from my pull list, but that would only be one book. Wow.
Honestly, I've learned that, no matter what the fans think and feel, Marvel will always do just whatever the hell they want with their characters...and 85% of the fans will buy it up anyways...so the company makes their profit, the fans (most) complain about it, but still buy it, snt he ones who truly hate it, just quit reading it.
If you are asking what I think, I think they shouldn't kill MJ. I also think they shouldn't have unmasked Spider-Man or had him eat a guy's head/soul. I also don't think they should have had Norman knock up Gwen...but they all happened.
Let them do what they want...it's what they're going to do anyway.