I wish I hadn't marked this as solved, because I have thought about this some more, thinking through the impact to our analytics. Unless I'm wrong, and I hope I am, if I purge inactive leads it will impact even last week's data.
Let's say I sent 100k emails last week with a 3% open rate. Today, I find 7000 inactive emails. If I purge them today, last week's open rate is now 3.2% (3000/93,000). All the 2013q3 metrics I put in last quarter's report to management, is going to be very different from the 2013q3 metrics I put in this quarter's report to management. No bueno.
The reality - inactive leads have to be kept in our database if we want to protect the integrity of our data. Someone tell me I'm wrong.