You are right. That is currently not perfect and returning before the workflow is done is not possible.
I really want to avoid adding more “flags” (there are already too many) esp. if they do not do anything at all in very many workflows (literally in all which do not have a webhook). On top do we not just have to consider the actual response-body also the response-code (Webhook - modify response code based on criteria [GOT CREATED] - #3 by GaRe) and response-headers. All of them should be able to be set dynamically at a later point. So the “flag” would also not help in that regard.
We do not have the perfect solution for that yet but something which seems to be more suitable would be a specific Webhook-Response-Node. On it all the response data could then be set accordingly, as soon the first node of that type gets hit, it returns the data and that allows then still the workflow to continue executing even after the response got send.
Does that make sense?