I don't understand. I had 1000 zclassic before decrease. Now I have 1000 zclassic, and 1000 zencash. If I sell my zclassic will I lost zencash? and what you think, what will be price for zencash and zclassic after 30 may? I don't know what I should do...

No if you sell zcl, you will not lose your zen. Hold both.