Self rescue is an excellent topic. It's a subset of the broader topic of failure analysis. And we all should think it thru. The details are going to vary based on your climbing method and details. Basically... ya step through the entire system, piece by piece, and ask what ya do if THIS goes wrong. Or if a mistake is made. For example, ya don't need to consider dropping your sadde... its not droppable... but ya do need to consider anything ya can drop. And if it has a backup, what if you drop that too? After all, your hands might be frostbitten from the cold after going unconscious for a while after the heart attack. We should never assume we are 100%. In the real world, problems like to find each other.
In my JRB system, here are the failure modes I am aware of and have chosen not to mitigate:
1. If the tree fails, i am dead.
2. If the climbing rope snaps, i am dead. (And so I use ropes with MBS 20x the working load).
3. If the fixed portion of my saddle fails, I am dead. (This doesn't include the bridge, because its adjustable... but it does include the bridge loops.
That's it. If anything else fails or gets dropped, i am good and can self rescue. That includes any carabiner or anything moveable or adjustable like a friction hitch. Even my bridge could snap and i go nowhere. The beauty is that i don't need any extra stuff to execute the self rescue after the failure. Because everything i need is already an attached, as a non droppable part of my system. This includes one spare carabiner and a small length of cord, which are connected to each other and me.
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