I don t understand one thing - if all the Mex available will be blocked for selling but we will be able to put it in liquidity pool and other people will be able to buy it, how we will get the full Mex back when taking out from liquidity pool? From where will come the rewards?

During an EGLD - LKMEX liquidity deposit into the EGLD - MEX pool, the amount of LKMEX is sent to a contract that keeps the amount of LKMEX sent, mints the same amount of MEX and then deposits the liquidity into the pool. When the time comes to withdraw you receive LKMEX with the same metadata as the deposited LKMEX (same vesting period). Regarding the question "From where will come the rewards?" you can see the block rewards for year 1 here: http://maiar.exchange/mex-economics.pdf