Of all the RPs I was in, only one ran to its conclusion, although one other received an epilogue.
Phyrric was never a big thing - hardly any of the posts exceeded two paragraphs!, - but it was part of a series run by the OP, and in this particular incarnation, another player ran a fairly proactive antagonist. I tagged along, as a mechanic caught underfoot, who managed by her presence to screw up someone's plans (which seemed like sufficient comfort as she laid dying, strangely).
World of Ilidia, meanwhile, was wrapped up so as to set the stage for its freeform sequel - although this never did quite get off the ground. (That was prior to its reboot on these forums, which I quite regrettably missed. Also prior to my learning how to establish a scene of relevance to the plot, as opposed to merely acting within a GM-established one. Caveat: I have not verified lately whether I yet have this ability. Small steps towards authorship...)
If we include evolution games and their ilk (i.e. writing exercises with audience participation), the number of 'concluded things' goes up to... three or four, at a guess, depending on whether ex post facto pronouncements of death count. (Even those are hard to come by! I certainly never made any of the ones I should've.)
There is a strange joy in acknowledging events from previous, now-inert RP on, typically, a character sheet for something new. Well, a sequel or reboot, usually. (My crack designated marksman, for instance, who was originally as much STR-based as WIS-based, but turned out to be the 'resident skeptic' as soon as the team became involved in intrigue.)
But there is that time I took a nanobot-infested alien grasshopper-thing (from the Virus RP, in which making posts accumulated currency with which to buy in-RP upgrades), and decided that he'd been dropped in a wormhole by a specific wayward CUSTOS agent (creation club - long story...), so that he'd be beamed as radio waves to Earth, collected by SETI, split across several hard drives, which then fell off the back of a truck. In this way, one chunk of his distributed consciousness would arrive in my other character's scrapyard, and there be woken up. The other players all also played as nascent sapient AIs.
By which I mean my friend and no-one else. That RP made it as far as page 2.
Journeys needn't reach their destination. But it helps to have one in mind. And to enjoy the milestones actually achieved.
Maybe I should have lead with the pithy saying / thesis statement? I haven't settled on a protocol for these things.