An involuntary delisting does not cancel the shares. Trading usually continues on otc-markets, often on the pink-sheets, with wider spreads, no options market, no margin eligibility, and forced selling from funds whose mandates require listed securities. That forced selling is the reason the largest drop often comes before the delisting date, not after.
Voluntary delisting happens in a going-private deal or a merger, where holders receive cash or acquirer stock and the ticker simply stops.
Example: a fund holding 4M shares must sell on delisting. Average daily volume is 600K shares. Liquidating even at 25% of volume takes 27 sessions, and the market knows it, so the discount arrives immediately.
Related: listing-standards, deficiency-notice, otc-markets, pink-sheets, going-private