What are the risks of keeping my Delphi projects on a portable hard disk?

What are the risks of keeping my Delphi projects on a portable hard disk?

I have a portable hard disk with half a terabyte where I keep just about
all my irreplaceable data. However, I was advised long ago to keep source
code on the local disk because of possible breaks and also possible
changes in drive letters. Also, if firing up the IDE and the disk isn't
there, it would fail to load all the libraries.
So ultimately, what are the risks of keeping all my source code on a
portable hard disk and working with it from there? What could go wrong?
I'm not asking should I or not, I'm asking what might happen if I do.