If you fail to climb across the dangerous climb you end up in some random ridge now, where if you are alone and without a dm you might as well log until a reset.
While I understand the idea behind this, the ridge should be removed. If you want to make it more dangerous have the player fall into a more open area of lower dark.
You can still climb down from that ridge and make your way back the long route. I think that on the grapple area itself you are given a warning that it is a dangerous climb. Always carried two ropes when I played a PC that lived out there myself in case I rolled a 1 on the climb check.
This just literally happened. You cannot climb back if you fail the dangerous climb.
There's a way to climb out, granted it does require having a second rope with you. I can figure something else out but I really dislike the original way it worked in which PCs would just "fall into the Lowerdark" (in a spot that doesn't match up also).
Maybe you could just add climb placeables to the area for those alone and without two ropes. Like stepping stones up but with higher dc to climb up.