If the agent does not answer a call during the allotted time OR they "Ignore" the call they will be placed in RONA (Ring on no answer). At that time, the caller will be placed back into the queue, until the next available agent.
You will also get an IM that let's you know you have missed a call and are placed it RONA. And you will also get a email in your outlook, letting you know you have missed that call. RONA will also show up in the dashboard
To accept calls again, the Agent will need to change their presence in Skype for Business to "Available"