Humans eat meat, so there being 8.1Bn people slaughter of animals for food is done on an industrial scale. Finality for farmed animals is going to happen as their very reason to exist is as food. The wild animal bounty is hunted or fished.
The only question is how that end is carried out. How humanely done?
The natural world is not so kind. Death comes from predation, disease, parasites, dehydration from lack of water, starvation, and rarely old age. Few are "humane".

The natural position for humans has always been as meat eaters. Even chimps eat meat. Humans that don't eat meat do it for religious or lifestyle reasons, though that may revert back in absolute survival situations. Being vegan/non meat eater is alternative to the natural way.

Some effort has gone into methods of industrial slaughter to be as humane as possible. There is a finality to life at that point. Just due to the pure volume there has to be some efficiency in the process. In Europe there is plenty of rules, regulation, policing, and investment, to be effective, which includes high levels of hygiene for human consumption. (I am an advocate of some of the smaller, more local, slaughter houses, that can have some of the highest animal welfare practices.) Some places in the world it is just more basic. And then where there is money some want to cut corners; which is a policing issue.

In a world of vegans there would not be any cows, sheep, pigs, or chickens. Nor many herbivores as they would be competing directly for our food. In fact there wouldn't be anything, including other predators. Humans don't tolerate competition well.
The reason we allow them, farm them, conserve stocks of them, is because they taste good.

Bacon butties taste fantastic.