Complex sentence: Estimates vary, but it is likely the corridor his forces opened enabled up to 250,000 refugees, including up to 25,000 men of the Ninth Army to escape from the advancing Red Army towards the west.
Split into simpler sentences: Estimates vary, but it is likely the corridor his forces opened enabled up to 250,000 refugees, including up to 25,000 men of 9. Armee to escape from the advancing Red Army towards the west.