Sometimes, yes. But the bug might not immediately be obvious (for example a memory leak) or cause data corruption, in which case you need to get a backup - and you probably don't use a backup without manual approval.
A good infrastructure will help you at every point, but it will still take time.
maybe because by definition you lose data on rollbacks? You can re-run all events/messages (if your company architecture supports it) but that gets more complicated, usually patching is easier and faster. Also, downtime.
