The Borneans have access to this as they had no indoor facilities constructed with RORA. On the original planning document for RORA, they outlined what the 2nd phase would look like and essentially, it was a mirror image of the building that was actually constructed in phase 1. As for re-opening, as much as I'd like to see it open again (purely for my own selfish, nostalgic reasons) i very much doubt it will happen because it would be a major let down for anyone who had just stepped out of RORA then went into the old house
I've only been 3 times but each time we got there before the zoo opened, grabbed a coffee, waited until the rope went back and then went straight to RoRA. 1st time, we had 20 mins to ourselves, 2nd time - last Saturday - we were in there on our own for almost an hour (fantastic) before anyone else came in, and 3rd time, last Sunday, were joined by just 2 other couples with the same idea (who were locals who'd apparently moved to Chester specifically for the zoo from Bedfordshire !). Similarly, we've gone back about an hour before closing when it hasn't been too busy.
I was actually thinking of opening up the outside, not so much the inside, although I'm sure that with the same internal structures as the main exhibit the old viewing gallery could be improved greatly, rather than being the bare landing it once was. When it's quiet it's fantastic, but one of the biggest gripes about RoRA is that it gets much too busy and claustrophobic, and when that happens it's hard to see the animals. With the old outdoor island viewable again, that would help alleviate lots of those complaints on busy days.
