Complex sentence: In the 2007-08 season he became the coach for Estudiantes, filling in for Mariano de Pablos, who had been fired due to negative results, and succeeded in keeping the team in the Spanish league.
Split into simpler sentences: In the 2007-08 season, he became the head coach of Estudiantes, filling in for Mariano de Pablos, who had been fired due to negative results. He succeeded in keeping the team in the Spanish league.