I'd also suggest that there are outstanding teachers in the government AND the non-government sector. (Having taught in both)
Independant schools will continue to grow as long as people see the need for them.
And breifly on the primary/high school debate: there has been a trend for non-government r-12 schools to develop a 'middle school'. This is essential creating a 3rd sub school and runs from year 6 or 7 up to year 9 or 10. DECS is a long way from being able to move to that model, given the massive infrastructure it would require.
Primary schools (r-7) pride themselves on being able to prepare students for high school, and I believe they will always have their place.