Ideas for warlock consequences for disobedience

So, one of my players want to play a warlock with eldritch godlike entity as a patron. His idea was that he doesn't like the pact hs is into and has to use a specific herb which conceals him from his patron. And if he runs out of the herb, the patron will attempt to establish dominance.

He specifically asked not to be killed outright (which I wholeheartedly agree with). And I do not want to mess with his character's mechanics (as, for example, not letting him take warlock levels or take away any of his abilities).

What are ways in which his parton could react in order to punish the PC or "bring him back in line"?