As far as my understanding goes , Interfaces which are part of a Port Channel is exempted from STP calculation . I believe , configuring bundling ports to a Port Channel can be considered as a quick way to use all the trunk ports connected .
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Well if it's the only remaining channel link, the port-channel goes down. If not the only remaining channel link, the port-channel continues without it. As you note, you lose bandwidth and I believe traffic will be rehashed across the remaining channel links, which can result in less optimal load distribution.
Protocols like STP or a routing protocol shouldn't see a link outage or flap.