Thankfully there are many other tools available for spriting and pixel art. Aseprite
is a well known desktop software, and https://www.pixilart.com/
is another very powerful online sprite editor, with a lot more community-oriented features.
Also, the Piskel editor will still be available here, only accounts will be removed.
Finally, Piskel is fully open source, both the editor
, and the website
. Anyone who wants to duplicate the project and run another instance of Piskelapp could do it.