Can a court order the seller to pay me even if their business has since shut down?

Yes — a court judgment is against the seller personally, or the seller's corporation, for the money owed, and the fact that the specific business that was sold has since shut down doesn't erase that judgment or the seller's underlying obligation to pay it. The judgment stands regardless of what's happened to the business itself in the meantime.

What actually changes is how easy the judgment is to collect. Standard enforcement tools generally remain available against a judgment debtor's other assets and income, whether or not the particular business that was sold is still operating — the judgment isn't tied to that specific business surviving. That said, a defendant who genuinely has no remaining assets or income to pursue can be a real, sometimes practically impossible, recovery problem even with a perfectly valid judgment in hand. Before assuming a judgment alone solves the problem, it's worth having a realistic conversation with your lawyer about the seller's actual current assets and what collection genuinely looks like.