Dropping from a sanctioned event mid-draft
Players who drop during limited events own the cards that they correctly have in their possession at that time. This includes any unopened or partially drafted boosters.


Like the rule says, if you drop, you keep any unopened or partially drafted boosters. Even if you pack two mythic rares.

If the rule is not convincing enough, here is a Level 2 judge's interpretation of it:


  At any time, you can take the pack in your hand, any cards you have drafted, and any unopened packs you have yet to open and drop from the draft. There will be no repercussions from Wizards for doing this. We don't try to replace any of those cards, the table will just continue drafting with one less player.


Another L2 judge by the name of Nathan Long wrote an in depth article on the subject. It agrees with everything stated above. On this Reddit thread, Toby Elliot chimes in on the subject. Toby is in charge of tournament policy, and he is also a L5 judge.

While it is totally within the rules to grab your pack and drop, the tournament organizer is not obligated to accept your money in the future. My local tournament organizer warns players that they may be banned from participating in future tournaments for dropping repeatedly. The threat is not empty; they actually follow through on some occasions. Talk to the tournament organizer before dropping.