This is also an issue with some TV clips (not just radio) where get_iplayer tries to download a non-existent "final" segment and think it fails.

Removing the radio check in the source code results in a usable and complete file, so the quick fix is probably just to treat the final segment missing as a non-fatal error for *both* radio and TV.  

See https://github.com/get-iplayer/get_iplayer/issues/315 for details.

Perhaps, but probably only if this problem starts to appear in HLS streams for broadcast programmes. First, I'm already dropping any formal support for clip archives like School Radio. More particularly, DASH streams get special consideration for final segment because the segment lists must be generated, and even the BBC media players sometimes have the segment count off by one. But in your case, the BBC screwed up in production for that particular programme. Segments can be up to 10 seconds long, so while ignoring your last segment makes sense because it is so small, that isn't always the case. It's also not possible to know if a different stream has the complete programme until you try them all. You're still left with a playable file in any case, though it will be the last (and probably lowest) stream quality that was attempted. You can re-download with --tvmode restricted to only the recording mode desired.

Implemented in 2.98