We have already seen how can be a relationship between a Warlock and a Patron
They are full of good hints and plots for your campaigns.
Let's see what would happen when the Warlock disobeys openly to her Patron's orders or when by her actions she avoids to fulfill its goals.
The Patron lays a curse on the warlock.
The only limit to those curses is your fancy.
You can choose a mechanical penalty, such as:
- disadvantage to spell attacks
- targets of Warlock's spells have advantage on their saving throws
- disadvantage on Dex checks
- 1 permanent level of exhaustion
Curses last until the relationship is on a good way again.
If you think this kind of curses are too much heavy you can have the warlock to make a daily CHA ST, with a DC ranging from 13 to 20, according to the Warlock's fault.
The curse can be affecting only the roleplay instead. For example the Warlock:
- communicate only with gestures
- sees only in black and white
- suddenly chants old rituals, often when silence is important
- lose his memory
- receives false informations by his patron
Again you should consider a daily saving throw if you think the punishment is too harsh.
AGENTS OF THE PATRON
The Patron sends emissaries to the warlock.
They're both other Warlocks or typical creatures of the patron such as totemic beasts, demons, extraplanar creatures or anything else.
For minor faults they should be only a nuisance for the warlock; for example they can suddenly enter in a combat, casting a Counterspell to cancel a Warlock's spell ("Our Master Grazz't reminds you who's in charge, worm!"), or they help the opponent in an attack roll ("This is from Asmodeus'").
On major faults, the agents will seek the Warlock to attack and even to kill her ("This is the punition for who disobeys to Chtulhu's will!").
The Patron can force the warlock on a quest for it.
Again, the limit is only your fancy: it can force with tricks, menaces, intimidations, by magic or something else.
The worse is the fault, the harder is the quest.
If you think Warlock's power are like a divine consequence from the relationship with a Patron, then the flow of power can be interrupted if something goes wrong between them.
You can forbid spellcasting of one or more spells or the use of some powers.
Or you can rule his powers recharge after a long rest instead of a short rest or that the warlock can use them only after a CHA check, again with a DC ranging from 13 to 20.
Personally, I don't like this last form of punishment, but in a rpg anyone can choose what suits better for his game.