That’s probably more of a contractual / accounting issue than a VAT one! Would it be your money anyway – or when you sold the business, did the new owner effectively buy all its assets and liabilities – including any amounts that may be due from the management company?
Realistically, you can’t keep the VAT registration open just in case the management company may decide that you’re entitled to something at some point in the future! But if you do get income later, you’ll need to establish what the formal “tax point date” of the transaction is. That’s largely going to be down to the detail of the contractual relationship between you, the management company, the hotel (if different) and the guest(s) staying there – so not easy to advise on via a forum! If the tax point date is during the period you were registered, then you could probably treat it as an error in the quarterly return covering the tax point date and notify HMRC. If the tax point date is after the end of your registration, you would technically need to determine whether you were liable to re-register.