When you are child-less in the literal sense - the notion of leaving a legacy - someone to carry on with a tiny piece of your spirit is a moot point. I used to wonder when I got old, who would take care of me - have any interest in how or if I was managing? Now that notion itself is a moot point - because at this stage there is no prospect of greeting a 'ripe old age'.
In some respects, we get a preview of the feeling of losing someone when a beloved co-worker moves on to another position or city. In the beginning, their loss is deeply felt, their name frequently raised in discussion, their empty desk a symbol to remind you of the absence of that person. But sooner or later it happens - that desk may be filled by someone completely different - the inside jokes no longer shared - the echo of their name grows dimmer - and while they may roll fleetingly across your mind in moments of nostalgia - those moments become less frequent. You'll keep in touch faithfully in the beginning - share generously all of the goings-on...but that too will begin to fade - a natural letting go. As they say, no one is invaluable - we can all be replaced - at least this is what we often repeat in the context of our working lives.
I don't know if it is really important - the prospect of a piece of me living on and yet it is there - it is something one thinks about - the prospect of that fading that will inevitably occur, that struggle to recollect. Over time, everyone who knew me will move on and time will do its work - as it should be - it is only natural after all.