The math says there's virtually zero chance of recovering 'lost' coins (lost meaning the only way to get them back is by guessing), while there's a definite finite chance of losing the coins we do have. Therefore, at some point we'll need something new - granted, maybe far in the future!
Incorrect. It''s simple to add more granularity to Bitcoin. Once the total supply of coins is down to 2.1 million, then we can just add another decimal place and we're back to 21 million units.