I suppose there is a number of ways to do this, but here is a couple ideas to build on. Set up a smart campaign to monitor the original send. If the email is not opened in a specific time, pause in engagement and request a separate campaign/add as member - this would house the drip (with wait steps) outside nurture. Deployment on the 2nd campaign will filter and send on program status (not success). Have a trigger in this campaign to monitor opens. If they open, mark program success and un-pause in nurture. Another option - Providing you have "Not member of" filter set up in program deployment, you could set up a batch that looked at whom was sent the email, if they did not open (in a specific time) remove as member. Making sure your leads can run through the campaign each time, I believe they will continue to receive the same content until they open.
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