One of the nicest things about the Cattle Drive course is that there is no time limit. You move at your own pace -- fast or slow.
The Assignment Log is maintained by the forum moderator(s). I think it helps students stay focused. Sending an email may not be sufficient to keep you off the inactive list, but posting in the forum is.
The other good thing is that "once a student, always a student". We've had students return after a couple of years away without a problem.