Did the Corleone's lose the war?

On one hand they gave in to entering the drug business after saying they wouldn't. The Godfather was seriously wounded and never the same. His eldest son was killed, and it was still unknown if Michael could ever return.

However, according to the book and video game, they were absolutely destroying the Tatagglia family in the fighting. In fact I think the first clue that the Corleone's weren't just fighting the Tattagglia's was the fact that they were still fighting despite such heavy loses. Also the Corleones stood to make a huge amount of money with the drugs, and still kept all their political connections intact. And The Godfather got a promise that no attempts would be made on Michael, as they worked to bring him home.