My friend's Dynabar rope slider broke and had to self rescue in. To avoid this, I always check my slider line for wear and recently replaced it with 3/16's Amsteel Dyneema (green line in photo). At $1.08 per foot (US) I always buy extra and keep it my bag.
But what if the line does break, albeit unlikely with a line in good shape, anything's possible - maybe a slipped knot, who knows. I thought why not have a back up plan built into the bar. So I took the same Dyneema line (red line in the photo) and slipped it through the holes into the center plate with a figure eight knot holding the line in place.
If the slider line was to break, just retrieve the chicken loop and secure it onto the (red) center loop on the Dynabar. It's becomes fixed and no longer in a sliding mode, but at least now you can get back in if I choose, or just continue your session for the day.
Side note, I recently switched from the Powerwave Bar to the rope slider with rings. The rope slider doesn't lock in quite the same as the metal bar (jumping on the twin tip) but once I got used to it, I prefer it. The bar in waves was doing a number on my surfboard with occasional contact with the board. In one crash Powerwave bar and my board caused a 4 inch split on the deck. It's just more metal-hard objects to potentially ding the surfboard. Since I never unhook on purpose, I took it one step further and opted for the stainless steel rings over the roller pulley The sliders are smooth enough and I don't worry about extra wear verses the pulley-roller. The Amsteel line is inexpensive enough to replace.
I left the bungee on the bar in case I change my mind and switch back to the pulley, maybe to unhook, who knows.
Love the short leash (Cabrinha) too. Simply, simplify, less thingy's dangling and getting wrapped up on something.