That is not true. The upper bound is the combination of how much people will pay you for the bitcoins they mine, how much people value being able to transact (

That is not true. The upper bound is the combination of how much people will pay you for the bitcoins they mine, how much people value being able to transact (transaction fees), and the value of existing held bitcoin. Since mining is what prevents attackers from stealing bitcoin,the total value of all bitcoin in existence actually has a bearing in this. If no one were transacting and no coins were rewarded for mining, people would still mine just so that their existing coins remain secure.