Short answer. Quite a lot. Section 4 of Rule 12 lets the court order the pleading, or the relevant portions of it, stricken out, or make such other order as it deems just, if the party fails to obey the order or complies insufficiently.
What the law says
If the order is not obeyed, or in case of insufficient compliance therewith, the court may order the striking out of the pleading or the portions thereof to which the order was directed
Rule 12, Section 4 — Effect of non. Read the full provision →
Two triggering scenarios: disobedience or insufficient compliance
Section 4 covers two related situations: where the order is not obeyed outright, and where there is insufficient compliance — meaning some response was filed, but it didn't actually satisfy what the court ordered. Both scenarios trigger the same set of possible consequences, since a bill of particulars that is inadequate can leave the moving party just as unable to properly respond as if nothing had been filed at all. Treating partial or evasive compliance the same as outright refusal closes an obvious gap: a party could otherwise file something nominal, technically respond, and still leave the pleading just as vague as before.
Striking out the pleading, or the deficient portion
The court's primary remedy under Section 4 is to order the striking out of the pleading or the portions thereof to which the order was directed. This is a significant consequence — it can mean the vague or ambiguous allegations that were the subject of the bill-of-particulars motion get removed from the case entirely, effectively penalizing the non-complying party for failing to clarify what they were ordered to clarify, and potentially weakening that party's own case if the stricken material was central to it. Where an entire complaint or answer depended on the stricken allegations, the practical effect can be close to losing that claim or defense altogether.
The court's broader discretion
Beyond striking the pleading, Section 4 also gives the court authority to make such other order as it deems just. This catch-all preserves flexibility for the court to fashion whatever response actually fits the situation — which could range from a lesser sanction to something more severe — rather than confining the court to the single remedy of striking out the pleading in every case of non-compliance. A court might, for instance, give the party one final short period to properly comply before resorting to striking anything out, reserving the harsher remedy for genuine, continued defiance of its order. The choice between these options is left to the court's judgment on the particular case, informed by how serious and how deliberate the non-compliance actually appears to be.