The thing I think is a bit different for animals in that they can't fully understand what is going on and we can't explain it to them. And many have such short life spans. So IDK if you consider days MORE valuable because of that, or if you think of it as "near the end anyway".
But for all of us, as we age, we don't heal as well or as fast.
If you were loaded, and money is not an object, would you consider it humane to put him
through all that to gain another few years? Do you think he would want that?
That's the question. THEN, if the answer is "yes", you ask yourself "can I afford it?". But if the answer is No, don't spend all your cash just due to emotion without considering the impact on him.
(I know you're thinking all this already, Bear. So I hope that doesn't come off wrongly. Just thinking out loud.)