how many SACEURs continued their military careers in other posts after leaving SHAPE?
The post of SACEUR has always been seen as a very prestigious one held by a highly experienced officer nearing the end of his military career. Thus most SACEURs have retired from the military upon completion of their service as SACEUR.
There are, however, three exceptions.
The second SACEUR, General Matthew B. Ridgway, lacked the political skills of his predecessor and therefore did not always get along well with the European Allies, so in July 1953 President Eisenhower made him Chief of Staff of the United States Army.
General Andrew J. Goodpaster retired from the Army at the end of his service as SACEUR in December 1974, but when a cheating scandal shook the United States Military Academy at West Point, General Goodpaster voluntarily returned to active duty in 1977 and took a demotion in rank to Lieutenant General (thus from four stars to three) in order to serve as the Superintendent of his beloved West Point and help it carry out needed reforms.
In October 1993 General John M. "Shali" Shalikashvili, who had been serving as SACEUR for only one year and four months, became the Chairman of the Joint Chiefs of Staff, thus in NATO terms the United States' "Chief of Defence", which is the one post that is clearly superior even to that of SACEUR.