Is my loyalty programme status permanently honoured?

No. Loyalty status recognition is offered only on a per-cruise basis under the NCLH Loyalty Status Honoring Program. After your sailing concludes, your honoured tier will revert to the tier you’ve earned through cruise activity with the brand you're sailing on within seven (7) days of completing your cruise.

For example:

A Titanium Seven Seas Society member from Regent sailing with Norwegian for the first time will be honoured as an Ambassador Latitudes Rewards member for that voyage. After the cruise, their Latitudes Rewards status will revert to their tier based on their actual cruise history and points earned with Norwegian.