I am not sure I understand your question. Can you clarify what you mean by an extended vPC? And what you mean by "bleep"? Are you referring to the member links going down, the vPC peer-links, or vPC keep-alive links?
If you bring down one of the member interfaces of the vPC traffic should still flow without an issue, which is the advantage of vPCs and having the redundancy there. It should not bring down other member interfaces in the vPC bundle.
If you are talking about a vPC peer link failing then the keep alive link should detect that and then the secondary VPC peer will put down all the VPC member in order to avoid an STP loop.
From an ACI perspective, the key differences to note here are that relative to traditional vPC design, there is no requirement for setting up vPC peer-links. There are also no keepalives being sent on the management ports. The fabric itself serves as the peer-link.
Hope this helps,
Michael G.
