They might forget if you weren't that important to them but on other people it has a profound effect. One of my online friends (who also passed recently) used to frequently tell me about her best friend who was murdered when they were only in primary school as it affected her quite badly.
Similarly sibling dearest is still affected by her best friend's death when they were 9, though a few decades later it comes up a lot less frequently.
And for some people life doesn't go on for ages, they just kind of stall when a loved one dies and end up in a fugue state for way too long.
And I think you would have left quite the imprint on that poor kid that dragged you out of the pool if you'd just gone and died on them XP
Happy birthday for your actual birthday and yay for the surprise party and good conversations XD