Signing a contract by definition takes his future out of his hands. If he were my son, I would be advising him against signing. I am also happy more and more young players are taking their future in their hands. Signing a long term deal will limit his options. There's no two ways about that.
We are not really a club that makes space for young players (not saying we should be or can even afford to be). Although we give chances here and there, their pathway is almost entirely based on circumstance with an incredibly small window to perform. Not every young player can be an instant hit.
I think the club should warm to the idea of buy backs. Real Madrid do it very well. At least let the buying club be able to gain from the players development. Loans are bullshit.
The safety net of being a player in the Manchster United senior team setup is
huge though. What Garner is doing is gambling that he will develop by himself at a lower league club and eventually be bought back by a larger club, assuming he has aspirations to climb to the top. The difference between signing a long term deal with Manchester United is just so different than signing with Wycombe.
Not signing a contract just doesn't make any sense to me. The player already has a solid say in where he will go on loan. The only difference between a loan and a transfer is that he's "stuck" in the loan (now permanent) club and he is effectively on his own.
The only reason that makes a lot of sense is if there is no pathway to the first team here, AND he is skilled enough to guarantee a solid career. The first one is up for question, the second one is up for question. The club has spent a great deal of resource on Garner to help develop him since he came into the system. The option of a buyback means that the club actively forfeits control of development and a potential extremly valuable asset.
Now, it obviously worked out for a player like Jadon Sancho, but he went to a club that could guarantee him CL football. A lower tier club in the English system can't do that. Either way, he'll be contracted somewhere, United, Forest, Hull.
If he believes that he's better suited developing in the lower leagues and carve his own career from down there, that is all well and good, but that is a massive risk to take.