There some issue not clear to me regarding borrowing Smartcoin.
If I bought and hold some Smartcoin. Then the one how sell it to me have merging call or want to close the borrow position. Is it possible that the Smartcoin will be taken from me automatically by the blockchain (for the collateral)?
Not normally. If you hold a Smartcoin, you can settle it to retrieve an (almost) equivalent amount of BTS.
Borrowers cannot "settle" their position, they can only try to buy Smartcoins from the market if they want to close their position.
There is one exceptional situation where your Smartcoin could be taken from you in the future. If the value of the collateral drops below the nominal value of the borrowed coins, the coin is settled. In order to "reset" the SmartCoin, you might be forced out of your position. You will receive the available collateral in exchange, of course.