In case b they restart setup with $13K positions. Eventually price moves in favorable way and necessary "exchange" takes place.
There are really countless benefits, however there are substantial limitations for such transfers.
1) Both nodes must have 3 to 5 times more money to make such transfer - price can go not in your favor many times in a row
If they only have 5x times they can only get it wrong 3 times (50-10-13-16.9=not enough to go again) no to mention repeated fees and the hassle of coordinating an unknown number of times.
Strangers won't ever do this. And friends can settle amounts <10% of their free cash whenever is convenient.
edit: But I appreciate the spirit.
edit again: did I get the math wrong?