I've caught quite a few barbel trailing varying lengths of braid and mono attatched to barbless hooks which had gone right round and out of the fishes flesh, so fixed permenantly! Infact the majority of the hooks I have removed from barbel have been barbless.
Imo, the theory of a barbless hook falling out is flawed.
A barbed hook doesn't keep penetrating once it is fixed, a barbless hook will keep prodding about as the angle is changed and can come right through, often folding over as this one had done ....
The fishs body was trying to reject the hook and it had a very large disfiguring infected swelling which I doubt would ever get anything like back to normal if the fish was lucky enough to survive.
A well known angler and perch fishing specialist Steve Burk actually banned barbless hooks from his waters because they penetrate so deep. Because a perches heart isn't far down it's throat and very often perch are hooked there Steve said that barbless hooks often punctured the perches heart, killing them, hence his ban of them...food for thought maybe?
Personally I feel much happier using a micro barbed hook.