This is a hypothetical question really, but my cat is getting on in years and was discussing with DH.
A friend of ours is paying over a hundred pounds a month for her cat's treatment. Their cat is too old to be covered on insurance (or insurance was too expensive).
The cat is 13. I said to DH that if that was our cat, I'd let her go rather than prolong her life with expensive treatment, especially if her quality of life was impacted or she was in pain.
DH said we'd probably pay too.