[RPG] How to deal with a fallen cleric, gameplay-wise

Player's Handbook II (3.5) / Divine Conversion / p193

This is a sidebar at the bottom of the referenced page, which is part of a section on rules for retraining. If you don't have the book, here is the direct quote:

DIVINE CONVERSION

As noted in the Player’s Handbook, a cleric who grossly violates the code of conduct imposed by his deity loses all spells and class features and cannot attain any more levels as a cleric of that deity. All these penalties remain in effect until he atones. But what if he doesn’t want to atone? What if a cleric of Hextor finds new meaning and purpose in serving Heironeous after a dramatic conversion experience? Such a character need not become a multiclass ex-cleric of Hextor/cleric of Heironeous. Instead, Heironeous can simply reinstate the character’s cleric powers once he has proven his loyalty, talent, and ability.

A cleric who changes his patron deity must complete a quest to prove his devotion to his new patron. The nature of the quest depends on the deity, and it always clearly reflects the deity’s alignment as well as his or her goals and beliefs. To start the process, the cleric must voluntarily accept a geas/quest spell cast by a higher-level cleric of his new deity. During the quest, the cleric has no access to spells or cleric class features—except his weapon and armor proficiencies, which he does not forfeit.

Upon completing the quest, the cleric receives the benefit of an atonement spell from a cleric of the new deity. The character then becomes a cleric of the new deity and is inducted into the clergy during an appropriate ceremony of the DM’s choosing. After selecting two of the new deity’s domains in lieu of his old ones, the character has all the powers and abilities of his previous cleric level, plus the granted powers of his new domains.

This method is the only one by which a cleric can change his deity. The retraining rules can’t be used to accomplish this task—it is simply too substantial a change in the character’s identity (not to mention his source of power) to chalk up to a bit of practice in his off hours.

This answer essentially reflects the ruling already found in the Forgotten Realms Campaign Setting, but it may be useful to know it's also located in a setting-independent rulebook, just in case there are any sticklers out there.

1. Get a cheatsheet into each player's hands.

You know that godsend player, the one who always has the notecards? Key thing there: the notecards.

You've spoken to the group, and they got upset, but you know they cared enough to get the books in the first place. It's entirely possible that they do just forget, or maybe they're having a difficult time with the rules and don't know how to articulate it. Even if they read cover to cover (and maybe they already have), there's a lot of information to parse and remember, especially for new players. Even veterans forget rules sometimes! Still, fumbling through the book for basic rules is not time-effective. My solution is to create a cheatsheet. This has helped me as both GM and player.

Figure out your most commonly used rules. Type up these rules and print a copy for each player. Try to condense them as much as you can. Strip them to their bare bones so players can find the information they need at a glance. Also, since you'll be distributing the same page to everyone, concentrate on rules that everyone uses. I'll discuss character-specific rules later on.

It's just more practical for you to make the cheatsheet. If they don't have the rules down yet, they probably don't know which ones are the most important. You likely have a better grasp, and you're also the one who wants more efficiency. The best way to ensure that this happens is to do it yourself, and then the whole group will be on the same page.

For character-specific rules, though, it's best if the players do it. This spreads the effort around. Plus, you can use this as an opportunity to help re-familiarize your players with their mechanics. Sit down with them and help them make index cards or type notes from the book. Point out nifty features and answer any questions.

Assure them that it will make their lives way easier, because it will. They probably don't like book-fumbling either. They'll also be more likely to use their character's features if they're always right in front of them in an easily-digestible format. It's hard to achieve your full potential if you don't know where to find it. The key thing is to emphasize how useful it will be for them (in character and out) if they do this, not how much worse things will be if they don't. Make it about them and their potential fun, not your frustration, to avoid further souring.

It's awesome that the Battlemaster Fighter took the initiative, though. If this is something he enjoys doing, you could enlist his help! I'm this player in my own groups, even when I'm not GMing. I love having a cheat sheet, so if I'm making one anyway, why not share? At the least, use his notes as an example (if he's okay with it).

2. Make use of existing resources.

Cheatsheets you make will be the best-tailored to your needs. That doesn't mean you shouldn't use ready-made tools on top of that. People often share their own tools if they think they're especially useful. If you need something specific, search the web to see if it already exists. There's no guarantee that what you find will be useful -- again, you know your own needs best -- but it never hurts to try. If you hit gold, that's time and effort saved.

For instance, here are some form-fillable initiative cards that provide a quick reference of initiative order and PC skills, traits, and actions; here is a larger, longer version of a similar concept. Here's a site that generates spell cards. ENworld has many sheets available. It only took me a few minutes to locate them by searching "5e spell cards," "5e initiative cards," and "5e character sheets," respectively. You'll be more successful if you already know what you need, but you can still try searches like "5e game resources" and "5e player print outs" if you're looking for tools in general.