You might be right. In some places it says the offer expires, in other places that the exclusive negotiating period between TNZ and NZ Govt expires.
Either way, I expect TNZ will get a higher offer from elsewhere - which they may or may not go with.
And if they did ever come back to NZ Govt and ask about the original $99m I'm sure the NZ Govt would happily give it to them to keep the cup in Auckland. Unless they had already spent the money on a cycle bridge.....