When you delete the chapters of your series on Webtoon, without deleting the series itself, it'll go invisible until you start publishing again. That way you can make new chapters, the website will expose you as a new series, without losing the numbers you already made. You can also change the name, description and such and most of the time people won't recognize it as the same series, maybe just because of the artstyle only.
I won't recommend leaving the old version active as it's own thing because some readers don't get the memo independently if you write it with big letters that the series got cancelled on said oupload and you're publishing it somewhere else. For authors note and stuff, I believe social media should be a better place to do it, some readers may complain about doing something that is not the series even if you're doing it as a separate thing or after the episode within the same oupload.
