If there is only one known flaw in the bitcoin code, that will be THE flaw that will be exploited one day. It will always be prone to exploitation. Bitcoin’s final block is estimated to be mined in around 2140. Do you really think someone is not going to come up with a brilliant invention that can harness unlimited energy for very low cost? Even if someone finds a way to harness unlimited energy in the year 3000, it is still a problem for bitcoin. Remember, longest chain always wins.
That bold part isn't correct that's around the year the last mining reward drops into a block before mining rewards cease. Blocks themselves will continue to get generated well after 2140 but miners will only be taking in transaction fees from them.
The chain still grows and you have quite an uphill battle to mine 600K blocks made between 2009 and now followed by the ~600K * 12 blocks that will be mined between now and 2140, with just an energy source in Sri Lanka esprcially when there's a lot of governmental bureaucracy and politics and red tape preventing people from mass-utilizing any energy source that's not middle eastern oil.