I don't thinks they can delete permanently.
Even you disk is broken, its data can be restore, not to say that google or other internent company may store your data.

Normally clear your browser history and cooikes would be enough safe.
Go to browser setting, find privacy option, clear hisotry and cookies manually.
You can also use some free decent clean software to do this.
Yet Another Cleaner: Cleans fast and deep, include registry and privacy data clean http://www.yac.mx/
Ccleaner: efficient to clean junks and uninstall softwares https://www.piriform.com/ccleaner