In the first option, if the observer node goes offline then flows will stack up waiting for it to come back, but if the code is structured correctly the txns will still commit to the ledger and business can still continue. The flows being pending will just reflect the business reality that the workflow has a stage yet to complete. It's subtle and tricky to get right because you have to ensure that the ordering is reasonable - for instance, if you send an email to indicate success after the regulator/observer is due to be informed, and that node goes down, the emails won't be sent. The flow framework could use some more functionality to support these more sophisticated workflow constructs (and/or integration with other workflow systems like BPMN engines?).
In the second option, if the observer goes offline, all business stops because you can't get the signature to make the tx valid.
WRT not going fast enough - yes the BN would be limited to the throughput of the observer node. I have a half written reply to your question about horizontal scaling in another tab :) Again, if the observer is the last action taken then flows might stack up during the day and drain at night as the observer catches up - not ideal but possible.
Re: red listing. By all means, please run with it. I just had a chat with Todd where I mentioned the need for us as a community to develop a party line on how tokens and regulations should interact; R3 has lots of great relationships with regulators so we might be able to help. And as you can see from this discussion, it's extremely likely they'll have to be presented with the complex technical tradeoffs involved.
The way AML laws are written regulators have quite a bit of flexibility to decide how they apply and different interpretations can have a massive effect on system reliability, security, scalability, privacy, reconciliation costs across national borders and so on. Everything is connected, so they may need to be brought into a multi-stakeholder conversation to thrash out an acceptable path forward. Pre-canned ideas would be of immense value then.