Symantec-Veritas
Back in 2004-2005, Symantec was looking for a "second leg to stand on". That is what led to the Veritas merger. Did the combined company struggle with its culture and identity? Yup, no doubt.
Was the foray in to Vertias a success? We can look back and say there was never a solid successful integration between the two companies (the largest tech merger at the time). However, during that journey a little thing called 2008 happened and the world went to hell in a handbasket. Did Symantec survive? Yes, they did. They had bumps along the way with RIFs and such. But they did not shutter their doors, nor were they gobbled up by Attila the Hun.
So from that perspective, the "second leg to stand on" strategy worked. And when the world changed again, the combined Symantec-Veritas became no longer needed and their destinies went down different roads.