Forever forever? What the heck does permanent mitigation mean?

In a recent op-ed for USA Today, mitigation banker Wayne Walker argues for establishing prairie chicken conservation banks, as a way to prevent the looming "train wreck" between environmentalist and oil/gas industry interests. It's a well-written piece that tries to spell out in basic terms, what mitigation is all about (EcosystemMarketplace renamed it, "How to explain mitigation to your grandmother"). Sometimes, though, it's deceptively simple. A big part of Walker's case is that offsets, like diamonds, are forever. He points to wetland and stream mitigation: "The logic of permanent easements is straightforward: Draining a wetland to build something is permanent -- not temporary -- and therefore the mitigation should also be permanent. The same principle holds true for the chicken. Impacts to it and its habitat are both permanent – the offset should be as well." Problem is, there's a clear difference between a permanent easement and a permanent offset, a difference Walker doesn't sort out. An easement is no guarantee of ecological function. Sure, the Corps will require an easement, but are they going to come back to the site in 50 years and check in to see what's up? To assess whether the wetland, stream, or prairie habitat is in a condition or performs such that it will account for the original impact the site offset? Maybe, but even if the Corps/USFWS did come around, would they require the bank to do anything about it? Should we even care? If the wetlands your local Wal-Mart paved over today are going to dry up or sink into the sea anyway in the next 20 years because of climate change, does it matter that the compensatory mitigation site Wal-Mart buys credits from function in the same way the wetlands currently do? I've walked through similar issues here and here. If, as Walker notes, the goal for all sides is "certainty," these are key questions if mitigation banking is to gain a sense of (ecological) legitimacy in an era of rapidly changing climates.