Loan players count towards the 25-man squad regardless of age.
That's only in the Championship buddy, in the PL they can be any age loan or not.
But yeah, Koumas on loan would be a waste. We might as well buy him, it's not as though Liverpool would want much for him.
I find Destan a curious case, I don't particularly want to see him leave as he looks like he has decent potential and even though he was clearly bought as a first team back up player, he ended up out on loan. Maybe they thought McBurnie was going to be out longer than expected, but either way, I'd not be selling him in case we go back down again.