Is it obvious when an elderly person is about to die? Please answer, I'm concerned about my grandmother...?

My grandmother is reasonably old (early/mid 70's). She doesn't seem particularly ill/weak, and is still living in her own home with her husband. She is, however, a heavy smoker, and has been since her late teens. Will it be obvious when she is about to die, allowing me to say my last good-byes? How likely... show more My grandmother is reasonably old (early/mid 70's). She doesn't seem particularly ill/weak, and is still living in her own home with her husband. She is, however, a heavy smoker, and has been since her late teens. Will it be obvious when she is about to die, allowing me to say my last good-byes? How likely is it that it will be a sudden death in the sleep kind of thing?
I'm sorry if this is a kind of morbid question, I'm just really scared that I will be caught unaware and I will regret not saying good-bye.
Thank you.
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