No, I completely agree that a heavily medicated short life wouldn't be fair on her.
I've been through this a few times...we often get dogs and cats with congestive heart failure left at the vets, as it can be expensive and hard work to sort them out.
Our last cat was 15 when she was left. The vet said probably 2 to 3 weeks before she'd be dead, if that. She was coughing and couldn't walk much and had a lot of swelling from water retention, but the moments that she was totally alive and healthy were so worth it. We tried Vetmedin and diuretics, on the understanding that if there was no change after a week, we'd let her go.
It took almost the full week to sort her diuretics dose out, and for the vetmadin to kick into action. I spent Thursday night sobbing that she was not going to make it. Friday morning she woke me up by jumping on my head. She ate a whole breakfast, and went out to play. Came back hours later and slept in the sun. She weed a lot, and didn't take to her tablets for a while, but she lived for four years after that. We let her go in the end because her joints were getting stiff and her cough was coming back, and she wouldn't have been happy to have her medications increased again, or spend the night in the vets. By year three her meds had dropped, so we knew that the end was nigh when she needed them back up to a full dose.
I'd definitely give your cat the same chance to respond, although it is completely your decision, and I'd totally respect it either way. It's tough.
We've had 7 cats and 5 Cavaliers' with this now, but it's always hard to make the decision whether to treat. I'm sure we'll be given a cat one day that just doesn't want to try, but so far, I'm very thankful for the meds!
FatCat sounds adorable. He may well help her out; having a healthy cat around always seems to help, provided he doesn't wear her out.
I really hope her scan is good tomorrow. Be prepared to be very shocked by the change if they drain her: but also that it doesn't hurt too much. Our wimp of a cat went through it seven times in the end, it's quick and she didn't mind too much. She loved running and playing afterwards, it looked like she'd just given birth!
I'll cross my fingers. And sorry for the essay!