Librespot does not exit upon network failure.This is a known bug that no developer was able to fix up to now, see eg Panic does not exit · Issue #226 · librespot-org/librespot · GitHub. One solution is to use a stable network connection.
If you think pulseaudio is the problem, then use ALSA mode: Librespot for LibreELEC only uses pulseaudio in Kodi mode, to stream to Kodi.
As for disabling Librespot during Kodi playback, it is an implementation choice: the user of Kodi (me) has precedence over Spotify users (my teenagers). If you value this feature less than I do, feel free to change the corresponding Python code here LibreELEC.tv/ls_player.py at master · LibreELEC/LibreELEC.tv · GitHub
Coders are welcome!