if the reload playlist option is enabled then it will save the playlist to reload.m3u (or reload.m3u8 on 5.25+) but is removed on a proper shutdown. i can't remember off hand what happens if the plugin finds that on load but i think there's a fair chance it will overwrite it.
if you're concerned about losing your playlist on changes then i'd install the latest version of
this and enable the option to save the undo queue on all changes (which would cover it). that will save copies of the playlist before change to %inidir%\plugins\gen_undo (where %inidir% is the location winamp.ini is saved out to)
-daz