If a file is incomplete on the network, you'll never be able to finish it. If only a few source has some parts, and many the others, you just have to wait... and wait... and wait, and maybe you'll be lucky and get the missing parts.
When starting a new download usually it's best to start that has the most sources.
aMule by itself will never give up on a file. If it's in the network, then it was once a complete file, so it's possible that someday the missing parts will appear again. Or not.
