What if I don't?

And (what) if I don't?

What will be the consequence if I don't do the thing you just mentioned? Usually said in a defiant or impetuous manner. A: "If you're opening up a business in this town, you can expect to pay 10% of your profits directly to the mob." B: "And if I don't?" A: "Well, let's just say you won't have a business to run before too long." A: "We want you to clear out of this property by next week." B: "And what if we don't?" B: "Then we'll have to initiate legal action against you."
See also: and, if
Farlex Dictionary of Idioms.

What if I don't?

Does it matter to you if I do not do it?; What difference does it make if I do not do it? Bob: You're certainly going to tidy up a bit before going out, aren't you? Tom: What if I don't? Father: You are going to get in by midnight tonight or you're grounded. Fred: So what if I don't? Father: That's enough! You're grounded as of this minute!
See also: if, what
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • And (what) if I don't?
  • plow ahead
  • add up to the same thing
  • amount to the same thing
  • amount/come to the same thing
  • or else
  • come with the territory
  • come/go with the territory
  • go with the territory, to