Technically though the last bitcoin will be mine by 2140, but we really don't know what will happen if bitcoin will go on and beyond infinity.

Just like any assets, there's a lot of opportunist in the market, buying when the price dips and then selling when the price is high. Greed only sets in if you still look for more profits and doesn't want to sell despite like having a 100% or even more ROI already. So bitcoin will remain if there is demand that will push the price to go higher.