Tank looks great, I'd love to see how it's grown in...
I have 2 tanks with a cork background myself, that are now 9 and 10 months running, and I can honestly say that there really isn't any decay happening. In fact, I'd say this cork is more tolerant of my soft acidic water here, than malaysian driftwood is. It's just not an issue. The way I see it, the cork will last longer than I will want the tank, I am sure.