But there may be a substantial issue here: once one has that sort of ending everything else in the story may feel trivial in comparison.

There's actually some explicit discussion of this in Worm's epilogue. That story had a relentless ramp of challenges always getting larger and larger until they were as large as possible (and then the story ended), but it was more of nireg n artngvir fvathynevgl naq gura yvir n abezny yvsr, vafgrnq bs oevat nebhaq n cbfvgvir fvathynevgl naq gura yvir n fgenatr yvsr.