I can't imagine that Google has the desire to create a completely separate fork of the Linux Kernel, independant of the rest of the planet's work. that doesn't mean that they will continue to make significant contributions back to the kernel, either. But I suspect, based on their FOSS track record, that we can expect them to continue to make contributions. Besides, If they want to continue using the Linux kernel source as the base for their own kernel, then it makes sense that they would want some input into the larger development process as a whole (which would mean continued code contributions). I mean, I think the only other option is forking, and could become quite a headache for them.