Assuming you are right and that we will miss a generation of creatives and AI keeps making crap, why can't the creative field regrow. AI won't remove creativity from human genes.
As people get fed up with AI generated crap, companies will start to pay very good money to the few remaining good human creatives in order to differentiate themselves. The field will then be seen as desirable, people will start working hard for to get these jobs, companies will take apprentices hoping they will become masters later, etc... We may lose a generation, but certainly not the entire future.
Of course, it is just one of many possible futures, but I think the most likely if you take your assumptions as a postulate. It may turn out that AIs end up not displacing creative jobs too much, or going the other way, that AIs end up being truly creative, building their own culture together with humans, or not.
Step 0. Some People make novel art like a jingle that is unlike anything yet.
Step 1. Early use of said jingle creates a buzz and generated good sales results.
Step 2. It gets copied everywhere and by everyone. It is now a meme.
This is the step I think where generative AI can help. Slightly transform existing art to fit a particular purpose. This lets businesses save money by not paying humans do this work.
Problem is we don't know where the next person or when this step 0 comes from... When we soak up all the "slack" and send all the "money" to the top because lets face it that's how it will work. The money "saved" from AI won't make goods and services cheaper by any significant measure. We will still have to pay as much as we can afford to pay.
As people get fed up with AI generated crap, companies will start to pay very good money to the few remaining good human creatives in order to differentiate themselves. The field will then be seen as desirable, people will start working hard for to get these jobs, companies will take apprentices hoping they will become masters later, etc... We may lose a generation, but certainly not the entire future.
Of course, it is just one of many possible futures, but I think the most likely if you take your assumptions as a postulate. It may turn out that AIs end up not displacing creative jobs too much, or going the other way, that AIs end up being truly creative, building their own culture together with humans, or not.