The initial error here in 𝓟—of writing repent instead of depart—was undoubtedly the result of anticipating the otherwise identical clause “and yet they would not repent” later on in this passage. Of course, the resulting “and yet they would not repent from them” is very unusual; we expect “they would not repent of them”. The phrase “to repent of something” occurs 66 times in the text (including six with not), but there are no examples of “to repent from something” (and, of course, none with not). Here in Mosiah 16:12, Oliver Cowdery seems to have corrected his error almost immediately (the supralinear correction shows no change in the level of ink flow).
Summary: Maintain the corrected reading in 𝓟, “and yet they would not depart from them”.