In preparation for root and all kinds of hackery for the Galaxy S5 it is always a good idea to have a safety net in place just in case you accidentally goof up and brick your device. Odin is the best way to recover from a disastrous situation. XDA member "krazylary" has made the Stock Rom available for download. You may want to go ahead and grab this and put it in a safe place as OEMs are often pretty quick to take things like this off the web. If needed you would open odin and click the PDA section and select this file and then click start. Pretty simple. Head to the link below to grab the stock image.
Via XDA