No need for buyback in your case because he wont be good enough and will never come back.
On a side note, our academy players arent better than roberts was at that age, he was tearing it up throughout all youth levels like Sancho, why do you think City spent so much on an 18 year old academy player, theyve never spent that much before.
Honestly, it shows that you havent watched Roberts play regularly if you dont think he is ready. Has surpassed every obstacle in front of him. If he gets a chance he can be one of Citys best players in a few years.