You can set the PATH permanently by adding that to your .profile or similar. ("Or similar" because it depends on which shell you are using. .profile should work for Bourne-compatible shells.) You might still want to investigate why and how your PATH got zapped in the first place.

A segmentation fault in nano is not "your" fault, it's the guy who wrote nano who apparently didn't take window size changes into account, or didn't know how to handle them properly. Now you have the source code so maybe you can fix that (-: but seriously, you might just live with not resizing your terminal, or use another editor which can cope.