Talking about distance

Over the years (and at a recent astro club meeting), I have many times heard
stuff along the lines of "the light we are seeing from the Andromeda Galaxy
left it 2.5 million years ago" followed by "so it might no longer exist".
The same issue often comes up when I tell folks that the Sun is 8 light
minutes away from the Earth, or that one's own hand held in front of own's
face is one billionth of a second away.

In what sense is it true that M31 might no longer exist, or that one's hand
might no longer exist, or that anything and everything might no longer exist
no matter how arbitrarly close we are to it? I have never been comfortable
with this "might not exist" stuff, and maybe it is because of some vague
ideas of Relativity and a "light cone". Anybody have any
thoughts/assistance? How should amateur astronomers be talking about
distance?

Dennis


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