It was partly but not entirely light-hearted. I do not think that humans will be limited to this planet much longer, and after that the solar system, and eventually the galaxy, will be left behind. And it will be entirely reasonable to leave our Sun behind when it eventually seems likely to terminate in some way.
I don't see that viewpoint as any different from the actions of Nature / Venus / Pleasure cited in the opening of book one of Lucretius in spurring all living things on to continue their species. Nature calls us to pursue pleasure as long as we are able, and life is necessary for pleasure.
Of course you are right that this is not a personal immortality for you or me or any particular person, even though I would expect lengthening of life span to go along with the technology of space travel. Not does a longer life mean "greater" pleasure. The theoretical maximum of "complete" pleasure is not made more complete by added time, but that does not mean that continued life and variety are not desirable.
Complete pleasure cannot be made more complete, but variety is pleasurable, pleasure is desirable, and pleasure requires life. All four observations are true, and none negate the others.
To me this gets back to the issue of "how long we should seek to live." I have always maintained that what Epicurus is saying is that life and variety are desirable, and the problem with worrying too much about them is that we do not have the ability to maintain them indefinitely. The hard limit is not 50 or 60 or 70 years but the "indefinitely" which is the logical hard limit that we have to accept.
But if we can expand healthy life to 100 years or 150 years or more there is no reason not to do so, and I think it would be foolish not to. This is why I usually kick back at the "I am satisfied that I have lived long enough" sentiment, because in my view Epicurus is saying that life is always desirable when it can be lived with more pleasure than pain, and that point when pain predominates is a practical one of circumstance, not a theoretical or logical limit which is fixed by God or fate or even nature itself. If healthy life span can be extended by technology, anc we have already made strides in medicine to do so, it seems non-controversial to me than an Epicurean would do so. If Epicurus has had the technology, he would have cured his kidney issues and continued on leading his school til some other factor intervened.
To me the question of life span is a subset of the ultimate question of "what happens to me if I make such and such a choice?". If the result of the longer life span, which is available in some technological way, is more pleasure than pain, then that choice is fully proper.
I think my attitude here is why I have no issue with the Epicurean gods being real. I see no issues at all with Epicurus being comfortable with space travel any more than he would have had an issue with human flight. A logical extension of the infinite and eternal universe, and insomnia, is that infinite numbere of species of human-like beings, of "infinite" technological advancement, have existed for an "infinite" time into the past, and will so exist into the infinite future. Their technology would naturally be expected to be far more advanced than ours, and they would be able to maintain themselves essentially indefinitely in what we would consider to be a perfectly happy state. And that's a goal worthy of emulation.
I think Epicurus would say that what is real to us is controlled by what we sense, feel, and anticipate, but we have to keep an open mind that advances in technology over time will expand what we ourselves find to be possible to sense, feel, and anticipate. No one 500 years ago could reasonably expect the details of our technology today.
I can't imagine Epicurus taking the position that "if God had meant men to fly he would have given them wings." What we do know is that nature has provided pleasure as a driving force, and one of the ways nature expresses pleasure is in the continuation of species, and the desire to continue to live where more life affords continuing pleasure. This is not far at all from Lucian's space travel story.
So I would consider it non-controversial from an Epicurean point of view that future generations of humans would act to continue their species in the face of any and all threats, including the end of our solar system, just as all other living things do.