Delete Lead Webhook

Absolutely - webhooks are synchronous, so the next flow action in a campaign will not start until the webhook call itself returns.  Please remember that Webhooks are available only for triggered campaigns.  

I just want a SmartCampaign that has only 1 "What"... Lead Deleted ... then the Flow will be "WebHook".

That why no matter how the Lead is deleted... the Campaign will be fired.

But, I thought you wanted to notify the downstream system before the lead is deleted.  If you could explain your use case in greater detail, we maybe able to suggest some solutions.  What does the downstream system do?  What info would you like to send the downstream system from Marketo?

The downstream system is a CRM but not SFDC or Dynamics.  It uses the SOAP API to sync leads.

The use case is that a lead is deleted from Marketo.  So we want to delete the lead from the CRM. But the SOAP API doesn't provide information about deleted leads.  So a webhook would do the trick.

Jeff,
You cannot invoke a flow action after the lead is deleted, because the lead's attributes like LeadID will no longer be available after the lead is deleted.  This is why there is no trigger for "Lead is Deleted".  So your best bet would be to invoke the Webhook before the lead is deleted from Marketo.  You could store the result of the webhook call (ie, whether the lead was deleted in your custom CRM) in a custom field and delete the lead in Marketo only after confirming that the lead was deleted in the CRM.  This will help you ensure that both systems are in sync

Raj