Apple are currently on a roll with the Mac, its performing very well sales wise, better than it ever has. To kill the Air would be a very bad move in my opinion. Whilst i don't really have much evidence i strongly believe the Macbook Air makes up the bulk of Apples Macs sales. I'm basing this on
1) Apples refurb store online always gets restocked with Airs quickly.
2) When i bought my Macbook Pro in 2013 i asked the sale guy if they sell many of these, he said no where near as many as the Airs.
3) I have a friend who works on a support desk for internet for students at a university in the student accommodation (over 4000 students living on campus) They survey the students about their equipment every year, last September they noticed something odd. It use to be 90% Windows based PCs, 10% Macs. He said this time it was closer to 50/50 split and it was majority Macbook Airs.
4) When ever i see Macs in public its seems to be mainly the Airs.
I think the Airs pricing point now has made it just about affordable to most people to consider. Its £250 less than when i got my first Air in 2011. I really hope the Air stays around for a while yet,i prefer it to my Macbook Pro, i don't care about the Retina display. In fact on some things i do the Retina display is a pain, causes lag with the scaling it has to do.
Would be sweet if the Air had slight price drop again to make it more affordable like its had over the last few years.