There are plenty of companies for which vertical integration did not work out. Commodore (Amiga), Silicon Graphics, Sun Microsystems, Acorn and many others. Apple nearly died in the 90s.
But I am not sure if vertical integration itself was to blame. The PC industry itself is full of companies which where not vertically integrated but which are dead or simply had to leave the PC industry Compaq, Olivetti, Sanyo, IBM to name a few.
In many ways you could call the PC a failure from the perspective of the company that invented it. IBM made it, yet failed to keep up with the competition and had to throw in the towel. Hence the openness of the platform was not a good choice for IBM. They failed to capitalize on the PC. In this regard Apple is a more successful company. They invented the Mac and are still selling it.
The PC has not really secured any company. Compaq used to dominate, yet they lost. Likewise I am sure there will come a time when today’s dominating PC makers will get kicked to the curb and somebody else takes over.