What will happen if the 21st million block is completely mined ?!
1. Will bitcoin status change from "beta" to "full version"?
2. Will it collapse like other fully mined altcoins?!
3. Will it become fully stable like other fiat currencies ??
Please share your views on this!
You mean the miner fees will also rise since they will not be mining new blocks, only securing the ongoing transactions ?
It is clear that you haven't made any effort to understand how bitcoin works, or what the purpose of "mining" is.
The miners are creating blocks that set a permanent ordering of the transactions. The proof-of-work that they supply makes any attempt to re-order any transactions that are more than a few blocks deep in the blockchain extremely expensive.
In exchange for providing this service to the network, they are rewarded with bitcoins. Their reward consists of the sum of a block subsidy (newly created bitcoins) and all the transaction fees of all the transactions that they confirm in their block.
At the moment the block subsidy is 25 BTC, and the average fees are about 0.1736 BTC per block.
Every 210,000 blocks (approximately 4 years), the block subsidy is cut in half. The next reduction will probably be in July of 2016 when the subsidy will be reduced to 12.5 BTC per block. Then it will be reduced to 6.25 BTC per block about 4 years after that.
Meanwhile, as bitcoin becomes more popular, there will be more transactions, and those transaction may pay a higher value in fees. Eventually the fees in the block will surpass the subsidy in the block. It is difficult to say exactly when this will happen, but it will probably happen sometime in the next 32 years. Once that happens, perhaps we will stop calling them "miners" and instead use a name that describes what they are actually being paid to do. Perhaps something like "transaction processors".
The block subsidy will continue to be cut in half every 4 years until somewhere around the year 2140 when the subsidy will be 0.00000001 BTC block. Then with the next reduction, then subsidy will be reduced to 0 BTC. Blocks will continue to be created, and the "miners" will continue to receive the sum of the transaction fees as their reward, there just won't be any subsidy added into the block any more.
As for your specific questions:
1. No. The "beta" vs. "full" designation has nothing to do with the block reward at all.
2. It may collapse long before the year 2140, or it may continue long after the year 2140. That's essentiall impossible to predict at this time, and anyone that gives you any prediction is just making a random guess. You could get just as accurate of an answer by flipping a coin.
3. It will either be stable long before the last subsidy is paid out, or it will never be stable. There is nothing about reducing the subsidy from 0.00000001 BTC to 0 BTC that would suddenly stabilize anything.