See, for all those saying "it's not worth it", consider this...
You have a large dog who's in perfect health, around 10yrs old with another 4-5 years in front of her based on family history, but has a ranula (saliva sac) in her mouth that's preventing her from eating. She has a minor surgery to try to fix it (the easiest option, about a 30% chance of success but no chance of complications), but it comes back a couple of months later and is worse than before. Now they have to have another more serious surgery with imaging to guide it, but it doesn't catch all the salivary gland tissue because dogs' anatomy can sometimes be weird and unpredictable, and it pops up again but this time at the back of their mouth and might stop them breathing if not dealt with. Now they need the first surgery as an emergency, but a final fourth one (with more imaging) to get absolutely everything.
That's about £10k in surgeries, none of them more than £2-3k, because anaesthesia is expensive for large dogs (but surgery is often easier than for smaller dogs).
That's what happened to our Akita last year. The last surgery wasn't covered by her insurance, so we were about £3k out of pocket. Personally, I would happily have paid for the whole lot if necessary, she's part of the family.
We didn't have to make a decision on whether to proceed with surgery based on money while the insurance was covering it; that alone is worth it, because having a pet put down on the basis of how much you want to spend is a shit thing to have come back at you in the middle of the night when they're gone.
However, the point is that these things don't always come in one big "This is going to cost you £10k right now and have a low chance of success" easy-to-answer question, they're often piecemeal and complicated.
My question is: in the scenario above, at which point would you have said, "No, this otherwise perfectly healthy and happy dog's not worth the cost"?