House Rule: How to Get Rid of Clerics (& Druids & Paladins)

Here's how I'm getting rid of Clerics and Druids and Paladins in my OSE based game:

The classes are unavailable for both PCs and Players. Their spells - with the exception of Cure Light Wounds, Cure Serious Wounds, Commune, and Raise Dead - are available to Magic-Users. 

Randomly generated Magic-User spells on level-up are still generated from the Magic-User Spell list, so the spells have to be obtained through play.

Where a Druid or Cleric spell also appears on the Magic-User list but at a different level, use the spell level from the Magic-User list.

That's it.

The Cleric class illustration from the Mentzer Basic Set
(Larry Elmore)

You may ask "why?" Or you may not, but I will answer nonetheless.

The reason why I don't want divine casters in my game is threefold: I don't like easily available healing magic; I like to keep the spiritual/ divine element of the game less knowable and game optimizable; and in I find the whole blunt weapons + armour + siloed spells thing for Clerics pretty naff (this is obviously a subjective thing).

In general, I tend to prefer somewhere between this writeup on polytheism from A Collection of Unmitigated Pedantry and Black Streams: Cult of Ruin for my religion in my Old School Fantasy Gaming.

As for how it'll impact the game, I've added a Bonus Hit Point mechanic which I think will more or less balance out the lack of Cure Wounds spells.

On the DM side - where a pre-published module features a Cleric I will either convert them to a Magic-User, to some sort of Cultist, or a Fighter with religious inclinations (which ultimately is just another flavour of Cultist) as appropriate.

The Cleric class illustration from the Mentzer Expert set.
(Larry Elmore)