Lets assume that 10% of all the remaining bitcoins are lost every year. That's a ridiculous amount. At today's exchange rate that's a permanent loss from circulation of $882 million dollars worth of bitcoins. I think most people would occur that losses will be much less than that. But, for the sake of argument, how long will it take until there is nothing left?
10 years? Nope. After 10 years there will still be 7322247.24210000 BTC remaining.
50 years? Nope. After 50 years there will still be 108229.27935400000 BTC remaining.
150 years? Nope. After 150 years there will still be 2.874721060000 BTC remaining.
500 years? Nope. After 250 years there will still be 7635.6610000000 satoshis remaining.
1000 years? Nope. After 1000 years there will still be 0.00000000000000036705296286175683 yoctoBTC
Keep adding decimal places (and shifting over the decimal point), and you can keep losing a percentage of what's left and still have more than trillions of spendable units
There was an analysis done in July 2014 that found (at that time) there were a total of 2,745.22283996 BTC that were provably permanently lost:
https://bitcointalksearch.org/topic/how-many-bitcoins-have-been-provably-lost-at-least-675321
Many coins are lost due to beginners faults, especially in early days when btc was almost worthless. As we approaching 1k$ i think this percentage will be only less and less until become negligible values.
You'll never know for sure if some coins are actually lost except if those coins are not yours.