You cannot "find out" this with "absolute certainty". You mean, because the gov't says so? How do you know there aren't more such frogs somewhere in some boondocks? You don't.
By filling in your pond you know, beyond a doubt, the frogs will be gone forever.
In fact, all those frogs will be gone forever regardless, in a few years (depending on froggie lifespan). All animals die, didn't you know?
I guess what you are talking about is that not only would these die, but they would have no descendents, or their descendants would die as well. Uh yeah, so? It happens. It has happened to zillions of species and will continue to happen.
Why must every species of critter have descendants forever and ever?
One more thing: If these frogs are such great jumpers, won't they hop away when they hear the bulldozers coming? They're FROGS, for pete's sake, not statues! Just because you pave over their pond doesn't mean they'll SIT THERE, does it?
Either you would call in the bulldozers or you wouldn't. I don't believe all those who say they would, would.