I went to the Munk open house in November and I believe the percentage of MGA graduates who went on to a PhD was around 6% (they had published this somewhere in a booklet I believe). The vast majority (I think around 80%) went on to full time employment. There was a small number that entered MBA/JD programs.
It is geared towards those who wish to enter employment upon graduation. That being said, there are MRP options in second year and if admitted, I would likely keep my options open since I might still wish to enter a PhD program.