[BEAR.]

She shouldn't have.

I went over why Oakstar banished her and the kits here, but the gist is it was because Oakstar and the majority of ThunderClan believed Appledusk was responsible for the deaths of his son and Flowerpaw. He was repulsed by Mapleshade's deceit of their parentage (she fed the belief Birchface was the father) and felt betrayed. It was an act fueled by emotion, and he later came to regret his decision because the kits died in the process.

At no point were Mapleshade's actions justified. She murdered Ravenwing at the Moonstone in cold blood after Ravenwing exposed her treachery (revealed the identity of their biological father) to their Clan-mates, and led Frecklewish - a cat who felt personally betrayed due to Birchface being her brother - to her death.

Appledusk wasn't a great mate to Mapleshade, but you have to keep in mind at that point he had more to lose than her. Unlike Mapleshade, he wasn't obsessed with her. His love for his Clan and home was greater and he was already drifting away from her by the time she sought him out for refuge (see: he had some sort of relationship going on with Reedshine when she showed up).

He also had no obligation to help her. Despite her beliefs, she was the cause of their kits' death - she chose to go to the rapids with her kits instead of finding them temporary shelter outside Clan territory first. He denied loving her because he wanted to prove his loyalty to his Clan. Her arrival damaged his reputation and he didn't want to risk being exiled or lose what he had with Reedshine by admitting he still had feelings for her.

I don't think it was an easy choice for Appledusk, and I think he did what he thought was best for him. Did it leave Mapleshade in the dust? Sure, but you can't really blame him for prioritizing his Clan over a failed relationship. They didn't live in the time where half-Clanned relationships got off as easy as other forbidden partnerships did. The Warrior Code was actually held in high regard at the time, and Mapleshade broke several of them. Though Appledusk was selfish in his actions, at the very least he made some sort of an effort to save their kits from the river. He was far from perfect, but he didn't deserve to die.

Using the "Ashfur's in StarClan! Why can't Mapleshade be?" is kinda invalid considering he was coming from a place of hurt and genuinely believed Squirrelflight would be better off with him. He never actually hurt or killed anyone. Mapleshade revolved around "Revenge!!! How dare you put me in a position in which my kits were killed because I didn't think my forbidden relationship was imperfect!!!"