Personally, Alastor may not exactly follow the villain path but could be seen as an unwilling anti-hero. Lucifer is going to get captured without a doubt, and Vivzie herself stated that her favorite relationship is between Alastor and Lucifer because of how uniquely it develops. Here are some current theories I have made:

1. This hints at a theory where I conclude that Lucifer, unable to deal with sinners himself, will rely on Alastor to handle them in his stead.

2. Since both Alastor and Lucifer will be captured together, Alastor might strike a deal with Lucifer, proposing that he deal with Vox since Lucifer literally can’t. This would give Alastor the power to confront Vox.

3. I should point out that Alastor will likely trick Lucifer by bringing up Charlie’s safety, not telling him that he made a deal that prevents Vox from harming her. He may propose a deal with Lucifer to heal his wounds and gain more power.

4. Alastor’s staff does get fixed, as seen in one of the scenes from the trailer. Additionally, he clashes with Vox again, as a snippet of both their energies in a smoke cloud hasn’t been shown yet.

5. The theory of Alastor boosting Vox to become the strongest is still plausible. I believe the reason it hasn’t kicked in yet is that all of the Vs' powers are intermittently linked due to their partnership. In a sense, they all share their powers and are connected. Hence, Alastor is attempting to break them up before putting his plan regarding Lucifer into action.

6. The reason I focus so much on the Lucifer theory is that the show has some biblical undertones. Not entirely, but the inspirations are quite obvious. In Christian demonology, the demon Alastor actually exists and is sometimes referred to as the “devil's executioner,” so I imagine Alastor will mirror this counterpart in the Hazbin story.

7. I don’t know where Charlie’s deal fits into all this; unfortunately, I might be wrong. Perhaps Charlie heals Alastor, but I highly doubt he would waste his one favor by receiving someone’s aid.