No, the scheduler cannot preempt. The scheduler is called by the goroutine and given the opportunity to pause it whenever the goroutine does a channel send/receive or calls a non-inlined function or, of course, makes a blocking I/O call[1]. But the scheduler can't do anything if nobody calls it. To wit:

http://www.sarathlakshman.com/2016/06/15/pitfall-of-golang-s...

IIRC, work is underway (may be finished) to add a scheduler yield check to loops as well, which would fix the pathological case in that blog entry.

If your code is doing a lot of channel sends and/or calling a lot of non-inlined functions, it may look like preemption, but it's still cooperative. If you're writing latency-sensitive code this distinction should be kept in mind.

[1] Or whenever time.Sleep() is called, or somebody calls runtime.Gosched(). There might be other cases, would be happy to hear about it.