But in this alternate world both WotC and Paizo would have likely been far better off. A repeated criticism of 4e has been the lack of good adventures, which I'm pretty sure a close partnership with Paizo would have provided this missing element.
With Dungeon Magazine back in house, and it continually said over all these years that adventures are some of the worst-selling products... I don't think this lack was something WotC was concerned about.
Necromancer Games would have been ready with a book of alternate rules that would have put missing 3e flavor back into 4e, which would have silenced a lot of 4e critics.
But it's a lot of critics who either are still playing 4E anyway (and thus, WotC still gets their money even while the critics grumble), or it's critics who would move away from WotC to go to Necromancer (and thus, WotC doesn't get their money).
The number of people who are currently sitting on the sidelines and not playing 4E because they are just waiting until 3PP support products they might enjoy are more readily available to them (at which time they will jump in with both feet and give money equally to WotC and these 3PPs), is probably extremely small. Small enough that WotC isn't going to change their philosophy to cater to them. The money these people would bring in would just not justify making the change.