>Does a failed rollback mean (logically) that the transaction is still open and uncommitted?
Yes, it means exactly that until something else manages to close the transaction.
Generally that's done by noticing that the connection has failed, or a timeout has expired, assuming "roll back unless confirmed" is the default behavior (usually true, but not always).
The reason you might want to explicitly tell something to roll back is to shorten ^ that latency, or to wait for it to complete before doing something else that requires it to be gone.
Yes, it means exactly that until something else manages to close the transaction.
Generally that's done by noticing that the connection has failed, or a timeout has expired, assuming "roll back unless confirmed" is the default behavior (usually true, but not always).
The reason you might want to explicitly tell something to roll back is to shorten ^ that latency, or to wait for it to complete before doing something else that requires it to be gone.