I have a fairly old cat (she’s about 15 I think, but I don’t know for sure since she’s a shelter adoptee).
She’s in relatively good health now, but I was wondering that when her time comes is she more likely to just do in to a decline and then pass away/euthanized or can cats come down with “sudden death” conditions like a heart attack or stroke?
Cats will hide their symptons as long as possible, so they very often show a very sudden deline floowed by death.
Hard to predict for an individual cat, but I did have a (~13 year old) cat who didn’t appear sick at all, playing with me, just drop dead.
My experence also is that cats will decline very fast, perhaps an evelutionary trait, as if they are not 100% in the wild they are dinner, so they will stay at 100% no matter the cost till they have absolutly nothing to give, then it’s over.
Maybe not so extreme, but they do go quick, and my statment may have a grain or 2 of truth to it.
My mom told me that the cat she had as a youngster came running to her one day, and literally laid down and died. The cat was elderly for those days before people such as her ordinary family paid for medical care for cats, and had had many litters of kittens and lived a full life for a cat. So unless my mother imagined it or lied, it’s possible.
My best friend in HS has a Siamese who dropped dead of a suddent heart attack. She was hanging out on a neighbor’s porch when the family dog charged up, barking like crazy. Emma dropped where she stood.
Anything & eveything can drop dead suddenly. 
Then I should give my cat a nice pat on the head before I go to bed tonight.
Yep, they sure can. It’s not all that common, though, and we typically don’t call it a stroke or a heart attack. We usually just say they threw a clot. (Assuming, of course, that the animal died because an embolus deprived some vital organ of blood.)
It’s far more common for kitties to go into a decline, usually a pretty short one if there’s no supportive care. Most cats go into kidney failure if they live long enough, so I’d be far more concerned about that than about waking up one morning to find him suddenly dead.
And you should always give your kitty a nice pet on the head before bedtime. After all, you might not wake up.