Did you lost the whole Jailbreak or not ? If not try to install any .deb files and let me know if u can access the Root system folders via PC or Filza, ifile... ? If it totally broken try to use this link https://jbme.qwertyoruiop.com and Press Go and follow the popup steps. Then u will bring it back. If u can access the root system but only Cydia So u should remove and install it back. Google for latest Cydia version for your ios and download .deb file or just google looking for a few command lines that can fix it to back working via Terminal. All both works perfect