Example
Sorry, but I can't imagine people pressing this tiny button under the only one nickname accidentally.
Even if it happens, if you were a part of the clan your clan lead will send you an invitation immediately. If not... well, you should probably think about what was wrong and review your importance in the clan life. Again, I can't imagine my clan lead Taroni wouldn't take me back, and the purpose of quitting does not matter if I still love my clan.
Don't think it worth adding an additional popup.
How do you accidently press clans, scroll down to your name and press quit. They are probably lying when they say that but maybe it would be good for something like that for people to make sure that's their final decision.