Is this Sycamore still alive?

Possibly depends on if this was a variegated variety.

 

They definitely graft Norway maples. I was given one myself with the variegated leaf, like Pete mentions. It was a similar size to the one in the picture so it could be the graft failed/died and it's just regrowing from the rootstock.

If you do replace I'd consider a different species as they are really park trees and there are far better options for a garden. The sycamores locally all seem to have problems with the changing climate, many have just died or suffered massive dieback.