What happens if the seller can't produce a document they promised on closing day?

What happens depends on how important that specific document is to the deal. If it's a genuine closing condition — something the buyer is entitled to have in hand before the transaction can complete — the buyer can generally insist on delaying closing until it's produced, or decline to close at all if it never materializes. If it's more of a supporting document rather than a hard condition, lawyers often handle the gap through an undertaking: the seller's lawyer promises, in writing, to deliver the missing item within a short, defined period after closing.

Which route applies is a judgment call your lawyer needs to make quickly, since it affects whether you should actually proceed that day. For something central to the deal — a required consent, corporate authorization, or the minute book itself — insisting on the document before closing is usually the safer course. For something more minor, an undertaking with a firm deadline is a normal way to keep the closing on schedule without giving anything up.