@Ben1
Your old footprint library will not be wiped out, it will just need reinstalling into your new Kicad 8.
Personal libraries always need reinstalling at every major Kicad upgrade. eg. 5 to 6, 6 to 7 etc.
Open your Footprint Editor and select File > Add Library > Global then navigate to your personal footprint, library that is stored somewhere on your computer, using the list of places in the left hand column. When you find your library, highlight it and click “open”.
You can also install your library by opening Preferences > Manage Footprint Libraries and click the + icon (towards the bottom left) then click the folder icon beside the + icon and the same screen, as in the last paragraph method, will show. Find your library, highlight and “open”.
There is relevant information in these two FAQs you can find at the top of any forum page.
beginners-guide-to-personal-symbol-and-footprint-libraries
tips-n-tricks-when-making-personal-symbol-libraries
If you still have problems, please write here.