Reading this thread, I generally agree with what James has said, except for this last comment about the 25% royalty.
An operator, especially in today's market conditions, will do everything possible to keep a lease sub 25%. As a mineral buyer, I cannot value a property based on 25% when it is clearly leased at 3/16 and shows no signs of changing. Assuming this is a typical lease with no depth pugh, my bet is that the lease will be held for many years to come at the 3/16 rate. In that time period, all formations will be drilled and produced. There is the possibility that the lease expires after all of this production ceases, but that will likely be many years down the road and a new lease would be for other formations not currently being explored.