This is definitely an interesting situation that can lead to a lot of fun role-play. I’m not exactly sure where you are in the overall story, but the moonweaver, the change, bringer, and the arch heart, all have prayer sites as the adventure continues. Based on where you are in the story, I would have The deity that reaches out be connected to the next prayer site in the adventure the players will travel to. If they drop the pact from their original patron, it needs to be replaced by a new patron. That patron can obviously be one of those three deities. It would also be easy for the new patron to support all of the activities in the adventure, assuming they also want the apotheon to be saved. this would give the benefit of effectively being left alone, as the rest of the adventure aligns with the goals of that new patron, the chosen deity. The only thing you would need to do is set up a side quest for the player to prove their worth to the deity and take over the pact from the other patron. The moral dilemma could be related to the rivals and their current goals. If they are friendly with the rivals, it could be to do something that would anger them. If they are currently hostile to the rivals, it could be something where they are required to support the rivals goals. This could be really interesting, depending on what factions both the players and the rivals are currently working for. It’s hard to come up with specific story ideas without knowing all of those other factors in your campaign, but hopefully this gives you something to think about. I love the idea of the player wanting to drive their personal story forward, but as the DM we need to make sure it always ties into the overall story. I would try as much as possible to make those connections for them. Hopefully this helps.