Hi Col Klink,
That's an interesting thought! It could be taken as foreshadowing, I agree — or it could also be taken as Puddleglum being Puddleglum, with exactly the same attitude he's had throughout the book!
![Tongue :p](./images/smilies/10.gif)
Also, we find out in
The Last Battle that Rilian has been "dead over two hundred years" at the time of that story, so although there certainly are catastrophic events in that book, they're coming a very long time after Puddleglum's era. So perhaps Lewis wasn't meaning to allude to them there, but there's no way of knowing for sure, really.
I do find it interesting that at the end of
The Silver Chair Lewis says directly to his audience: "If ever you have the luck to go to Narnia yourself..." In fact, looking through the last chapter just now, I've found he also implies that Jill and Eustace are still alive in our world at the time he's writing — when they have an uncomfortable ride on the two Centaurs, we're told "But however sore and jolted the two humans were, they would now give anything to have that journey over again..." If he'd said "afterwards" or "later", that would mean that statement could refer to any time period, but saying "now" suggests strongly that they are still around to be feeling that way!
Similarly, a couple of times in
Dawn Treader Lewis heavily implies that Lucy too is still alive as he's writing this book and that he's even "interviewed" her to get the story — see the part in the last chapter where he quotes himself asking Lucy, and her reply to him, about the "musical sound" on the breeze from Aslan's country! Also at the end of
The Horse and His Boy, Lewis makes the wry comment about looking up Rabadash "in a good History of Calormen (try the local library)". That too seems to imply that he's thinking of Narnia and the surrounding countries as still existing — in their mortal "Shadowlands" form, that is — and potentially accessible from our world even as he's writing about them.
So from all this, I get the impression that it wasn't until Lewis wrote the last two books —
The Magician's Nephew and
The Last Battle (I gather he worked on them simultaneously) — that he made a clear decision to end the series with Narnia being destroyed. However, I can think of another passage in
The Silver Chair that sounds like a foreshadowing of the final book, as Eustace and Jill see Caspian resurrected on the Mountain of Aslan:
A great hope rose in the children's hearts. But Aslan shook his shaggy head. "No, my dears," he said. "When you meet me here again, you will have come to stay. But not now. You must go back to your own world for a while."
In
The Last Battle, of course, they DO meet Aslan again in his own country, this time to stay forever. But given all those other hints that Lewis didn't yet have that ultimate ending in mind when he wrote
The Silver Chair or the earlier books, maybe he simply meant (at least at the time he wrote those lines) that one day they'll die and go to heaven, without necessarily implying that it'll be any time soon or that this will be featured in a future book.
It would be fascinating to know just how the whole narrative of the Chronicles developed in Lewis's imagination over the several years that he was writing the books — when it was that particular ideas and inspirations came to him, and indeed whether he was originally thinking of ending the series differently — but I don't think he ever said or wrote much about that, unfortunately. Fun to wonder about, though!