How do you deal with an 'on the way out' pet?

Spent 3800 trying to save our cat who was renal failure at only 8 yrs, vet thought she was poisoned or ate something poisoned.
Her sister died a year later of the same, 3 months later decline, water iv injection daily. Very hard experience having them from kittens n they were thee best and never tore our things up. They also loved sushi and yogurt... they were top notch bird catchers too.

I feel for ya. They're like our furry kids.