If there is failure that prevents you from sailing back to shore (e.g., broken mast or universal), you need to derig the sail and paddle it back to shore.
The link below is a good video reviewing how to take apart a rig in the water to paddle it back to shore. It is a good idea to practice this on land every season -- who am I kidding, no one's gonna do it, but you should at least watch this video every season to refresh your memory. The key things to remember are (1) never ever ever let go of the board: it will float away faster than you can catch up to it; (2) make use of the various lines available (uphaul, downhaul, outhaul) to tie things to each other as you take apart the equipment; make sure everything is tied to the board in some way.
Self Rescue Video: https://vimeo.com/234383599
This is what it looks like when the tendon on a universal fails:
The tendon is a cylindrical piece of rubber that is connected to each section by a bolt that goes through a small hole.
A tendon failure will occur at those holes.
To prevent such failure, remove the bolt and inspect the tendon before each sailing season.
Here's a comparison of a bad and good tendon: