Yes, it's gone because you turned it off. However, someone turned it on in the first place. I suspect you may have the Accessibility Shortcut enabled. If you leave that enabled, you may find that Assistive Touch keeps getting turned back on. Go to Settings>Accessibility>Accessibility Shortcut. Make sure that there are no check marks next to anything.
About the Accessibility Shortcut for iPhone, iPad, and iPod touch - Apple Support
Also, the fact that you say "in this household" makes me feel the need to ask if you're sharing the phone with someone. If that's the case, you might want to discuss this with them.