Belief in reincarnation came into the modern Craft—probably via Theosophy—with Gerald Gardner.
Interestingly, though, there does seem to have been a word for 'karma' in old Witch vocabulary.
Karma in Sanskrit means simply 'act, deed, work,' from the verb karoti, 'he makes,' 'he does,' but has come to mean by extension the sum total of actions throughout one's various lives, and the effect of these deeds on one's present and future lives.
Similar in meaning is the Old Norse word ørlög, usually translated 'fate' or 'destiny.' Ørlög is the sum total of actions and events: everything that has gone on before which brings to bear on events of the present. To the Northrons of old, as in contemporary heathen thought, in addition to ørlög writ large, individuals, families, and nations all had their own ørlögs.
This seems an eminently pragmatic way in which to view the world. What is done is done, shapes everything that comes after it, and cannot be changed. But likewise, every new deed that is done lays down ørlög of its own.