After reach the 21 million limit, and every year there is some coins that are lost... won't this make the value of the bitcoin go up?
It is never possible to determine which bitcoins have been lost, and which are merely being held unused. In either case, it means they are effectively removed from the economy.
This means that they aren't being offered for sale on an exchange, nor being offered in exchange for goods and services. This creates scarcity, and as economists tell us, scarcity (in general) makes the value go up. It means that those who are offering to sell bitcoins on an exchange have less competition, and can charge a higher price.
Total bitcoins amount will never reach 21 milion, it will continue to approach the limit closer and closer. You can check wiki page for the details: https://en.bitcoin.it/wiki/Controlled_supply
About your question. Yes, these lost bitcoins will make other bitcoins cost more. But from market perspective, very big part of all mined bitcoins are not participating in transactions. We can treat them like lost bitcoins, and they also increase the value of bitcoin. But someday owners will spend them.