I am setting up the NIS slave server to automount the home directory just like its master server on suse linux (SLES 10).
Since the master will be the first to mount the /home on the client. I have not been able to mount the /home on the on the slave when the master NIS server is unavailable.
How can i make sure that the slave NIS /home is mounted when the master NIs is down and also how to sync the two home directories when both servers are now up?

Is the master NFS server the same as the master NIS server? The the answer is: you cannot.

What you are asking is: how do I do replication with NFS? The answers are quite varied, but in general: you don't. There are, however, two general approaches to the problem:

(1) as you suggest: synchronize the data between master/server. Some filesystems do this: CODA/transarc are the ones that come to mind. There is also block-level replication; DRBD does this. You can do it with rsync, but that's slow and you may lose several minutes of updates, depending on the size of your filesystem. (2) Use an external disk system that can connect to multiple hosts. Solaris and HP offer such products. Then you create a software "fence" so that only one computer can access partition X. If one computer becomes unavailable, the other can access it. The fence makes sure the first computer will not be able to mount the partition while the other has it locked. Examples include RedHat's GFS. Do-it-yourself methods also available.