I talked to the owlbear motehr and left her alive, the cub still spawned at my camp.
It hasn't yet shown up at my camp, but the last time in EA, it took it's sweet time too. This time, I had the tiefling party the first night and then the scene with Shadowheart and Lae'zel, so I guess, it doesn't turn up at scripted event Long Rests.

"We are all stories in the end. Just make it a good one."

Doctor Who