Do you need published papers to apply for a postdoc?
All you need to apply for a post-doc is a the ability to write an application - getting an offer is another matter.  Most post-docs will have their PhD and will have published (or at least submitted) one or more papers in the course of that program.  If your friend has not yet published or submitted any papers then he will indeed be at a disadvantage in an application for this kind of position.  Having said that, you've got to be in it to win it!  If he does not mind taking the time to write up an application, it can't hurt to apply.  In the meantime he should keep working on his paper and pushing for further progress with his co-author.  If he can succeed in publishing this paper in a high-tier journal then that will substantially improve his applications.