I have taken many Craftsy classes and never purchased any of the kits. I usually go to my stash and if I need more I can fill in by buying only the fabric I need. It is much cheaper and besides that you can get rid of stash and that is always a plus as far as I am concerned.
And I have gone back to classes I signed up for a couple of months later and if there is a problem (which there was once), you can contact them and they will immediately fix whatever the problem was. So, yes, you can take the course for a long time.