“ And now, behold, we are in your hand. As it seems good and right to you to do to us, do.”
Having admitted their reasons they acknowledged that, apart from disobeying the strict treaty-covenant conditions, Joshua was within his rights to do whatever he wished with them. There seems little doubt that one requirement was submission to the tribal covenant, although not as full members but as resident aliens (2 Samuel 21:2). They would be required to abjure their own religion and worship YHWH and submit to His Law. Their presence is referred to in the future and there is never any suggestion that they led Israel astray. They appear to have genuinely become Yahwists. Indeed as slaves they could be required to.