I don't think so. Eventually, with MCDRAM and iGPU on a smaller node Intel can make a big core x86 processor that's not only an SoC but also a good gaming CPU/iGPU. So I don't see the the big core consumer CPU going anywhere this decade.
As far as the number of cores, at 10nm even a quad core i7 is going to have a small die - at 7nm it will be tiny. There is plenty of room for Intel to add a variety of features to help make PCs more valuable. PC CPUs have great margins, so I'm sure Intel will do it's best to keep this segment as healthy as possible.
They still seem to think it's worth it to have multiple masks for desktop chips.
I can see them going all the way down to 1 mask for desktop chips before they get rid of desktop.
You have to remember that they are a fab company, and as long as they can justify the masks they will make desktop chips.
They could also just use the exact same chips for the desktop as for the laptop (something they do to an extent now).
Desktop is not going away because, as many have pointed out, its still very profitable and will be for the foreseeable future.