I think the bigger issue for the Magic and Wonder is where travel demand will be and how this Wish-class gamble goes. Disney will be stuck with the Wish boats for decades and between the wish and the new adventure class ships they have increased the number of beds available on
DCL by a staggering number!
If demand softens on the travel market, or Disney realizes they have too much margin erosion with a larger fleet, the Magic class boats will be gone sooner than if they can charge top dollar for DCL generally. Another open question is how viable will DCL be long term in markets that are not Florida. My view is that Disney knows they are a premium product in the amusement park space and a premium product in the Cruise Line space. They have to maintain that experience, which requires large margins to be able to do successfully over time.
The intersection of these items coupled with the maintenance costs will be the retirement date for the magic and wonder.