You'll get through the time when they are all gone. Trust me. It sucks, but it's the natural order of things and you'll be more OK than you think.
Start thinking and talking with them about it NOW if you think you will be providing or overseeing their care. I cannot stress this enough. Start planning NOW. NOW, NOW, NOW. It won't be easy to talk about. Do it anyway. It's easier than trying to figure it out as you go when it hits you in the face.
When it's all said and done, knowing you did you best for them will be more of a comfort than you'd believe.
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"