Maybe he wondered about players in teams that will become bot and not bot teams.
If I remember things correctly all players with a salary of at least $10000/week or in national team will go into free agency today if their manager retire.
Must be pretty few interesting players that got a salary of below $10k that are not in U21. For such reason I think that the problem of candidates for U21 retiring because their manager retire is very limited and only for smaller nations.
But maybe I misunderstood his question, the conditions for not retiring players or the salary of hot candidates for U21 ...