The SUSE Linux Enterprise Server operating system is a well-tested and stable system. Unfortunately, this does not prevent hardware failures or other causes for downtime or data loss. For any serious computing task where data loss could occur, a regular backup should be done.
For optimal security and safe work, you should make regular updates of all the operated machines. If you have a mission critical server, you should probably run a second identical machine where you can apply all changes for testing purposes before doing so on the real system. This also gives you the possibility to switch machines in case of hardware failure.