I just started learning Roku development so let's try to figure this out together.
In doc's i did find this: "
loop - If set to true, the video or video playlist (if the contentIsPlaylist field is set to true to enable video playlists) will be restarted from the beginning after the end is reached.Available since firmware version 7.2"So you could use this to loop your last video.Also, Video Node is where you should set this since Video Node is responsible for video playback.nextContentIndex - you can use this also and just pass index of the last video that was playing from the playlist.But i think it's not great idea since you have loop option for this.You should check https://sdkdocs.roku.com/display/sdkdoc/Video for more info .Sorry if my answer did not help you or if you already checked this options.