It is not really correct that "old hotels that are no longer operating" are being used as they are current hotels that are being "utilized" by the government granted as a goodwill gesture since the beginning of the pandemic. Sandals and Riu to name two. Once the pandemic deemed over, they will revert back into operational hotels.
But more than likely should you have to quarantine in Negril it would be in a section of your present hotel or in one of many of the sections or wings of currently open hotels being used for this purpose by the government.
The government run facilities have not been getting much use throughout the entire pandemic as the private sector facilities have been more than ample. On Christmas Day, from the Jamaican MOH website, QUARANTINE MANAGEMENT
Number in Facility Quarantine 1
One is not a particularly large number.