The process will try five times and then permanently fail; after you get the permanent failure notice is when it won't be trying any more. (I honestly don't remember what the difference is between the "this failed but will try again" message and "this failed permanently" message, but right now, you'll get up to five attempts to retry the crosspost before it gives up.)

If it permanently fails at the time you try to crosspost, you'll need to edit the entry, check the crosspost tickybox, and save the entry to start the process again.