Previous full-lifetime simulations of single-star multi-planet systems across all phases of stellar evolution have predominately assumed coplanar or nearly-coplanar orbits .
Here we assess the consequences of this assumption by removing it and exploring the effect of giant branch mass loss on the stability of two-planet systems with small to moderate non-Kozai ( < 40 degrees ) relative inclinations .
We run nearly 10 ^ { 4 } simulations over 14 Gyr for F-star , A-star and B-star planet hosts , incorporating main sequence stellar masses of 1.5 , 2.0 , 2.5 , 3.0 and 5.0 solar masses , and initial planetary semimajor axis ratios that straddle their three-dimensional Hill stability limits .
We find that the near-coplanar assumption can approximate well the stability frequencies and critical separations found for higher inclinations , except around strong mean-motion commensurabilities .
Late instabilities – after the star has become a white dwarf – occur throughout the explored mutual inclination range .
Consequently , non-Kozai mutual inclination should not be used as a predictive orbital proxy for determining which white dwarf multi-planet systems discovered by Gaia should represent high-priority follow-up targets for the detection of metal pollution and planetary debris discs .