A classical instance of the truism that “we are all works in progress” and therefore it is possible for even someone with a long history of apostasy to mend his ways religiously.
One of the verses in Parashat Chayei Sara (Beraishit 25:9) serves as the textual basis of the Rabbinic contention (Bava Batra 16b, incorporated by RaShI in his commentary) that Yishmael, despite having been banished along with his mother, from Avraham’s home, and then rejected his father’s teachings, eventually “repented” (in light of the uncertainty of what Avraham’s religious practices specifically were based upon the text of Beraishit, pinning down what “repentance” means in this context, beyond a belief in monotheism, is difficult to ascertain):