On client side, there is no explicit way to know which transaction is broken when there are multiple transactions undergoing. If your use case relies on transactional assumption, it may fail at some point.
On client side you know because you're setting the async-commit on a case basis.
All transactions work the same. When/If the server fails, some transactions (that you allowed yourself) may be not durable (or not replicated). But all things are still transactional.
It breaks the durabality for that transaction until a new transaction with synchronous commit 'on' completes or time passes for auto-fsync.