I started a thread on that subject tha'em.t raises the same questions:
http://www.gangsterbb.net/threads/ubbthreads.php?ubb=showflat&Number=761864&Searchpage=1&Main=29538&Words=%2Bliability&Search=true#Post761864
But, who else was available? Not Sonny, unless the only counseling Vito was looking for was "kill 'em." Not Tess or Clem, who were needed as operating officers. And not Michael, who wasn't in the Olive Oil Business at that time and seemingly didn't want any part of it. Vito had a real problem with succession planning.