Complex sentence: This plan did not materialize; wooden Maryina Roshcha was demolished gradually in 1960s, and the remains of it were cleared in late 1970s, preparing for the 1980 Summer Olympics.
Split into simpler sentences: This plan did not materialize, and wooden Maryina Roshcha was demolished gradually in 1960s. The remainder of it was cleared in late 1970s in preparation for the 1980 Summer Olympics.