Generally they lose the ability to swallow correctly. This leads to food aspiration which leads to infection. This becomes a cycle. Eventually (perhaps the first infection) families will choose not to treat and they will be kept on morphine as everything shuts down.

You could make more and more drastic interventions but at that point there is nothing of the person you knew remaining and there is no “better” way for them to die on offer. You will have a few days notice for loved ones to say their goodbyes and keep vigil if they want.

Unfortunately we don’t know how to do non-voluntary euthanasia. It’s just not a system we have figured out as a society/species. “Family consent” is hiding a lot of cost/complexity/trauma under the surface. The “decision not to treat” is effectively a soft form that offloads a lot of the complexity. So you need to present a cost/benefit analysis of how to move that date up and by how much. A much more traumatic process that only speeds things up by a few months probably isn’t worth it, but the earlier you aim for the more of the person remains.