When comparing boiling points of two ionic compounds, what bonding factors should you assess?
To compare 2 ionic compounds' melting point, there are generally 3 determinants:


Ionic Radii, smaller the ionic radius, closer the ions are to each other, therefore stronger the electrostatic attraction between them. (analogous to stronger attraction when closer to a magnet) A good example would be melting points of cations from the same group with the same anion (NB: LiF does not follow the trend, potentially due to its more covalent nature):


$\ce{NaF}\ -\  \pu{993 ^\circ C ( 1819 ^\circ F)}$
$\ce{KF}\  -  \pu{858 ^\circ C ( 1576 ^\circ F)}$
$\ce{RbF}\  -\  \pu{795 ^\circ C ( 1463 ^\circ F)}$

Charge of ions, larger the charge an ion has, more positive or negative the ion is, therefore there is a stronger attraction between ions. (analogous to stronger attraction with two stronger magnets in opposite poles) An example would be $\ce{NaCl}$ and $\ce{MgO}$:


$\ce{NaCl}\ -\ \pu{801 ^\circ C ( 1,474 ^\circ F)}$
$\ce{MgO}\ -\ \pu{2852 ^\circ C ( 5166 ^\circ F)}$

Ratio of ions, in most cases, closer the ratio is to 1 : 1 between anions and cations, stronger the attraction is. larger or smaller the ratio is, the more the anions or cations will have to 'share' or 'divide' the electrostatic attraction from the oppositely-charge ion, decreasing the melting point. An example would be $\ce{NaCl}$ and $\ce{MgCl2}$:


$\ce{NaCl}\ -\ \pu{801 ^\circ C ( 1,474 ^\circ F)}\ [1 : 1]$
$\ce{MgCl2}\ -\ \pu{714 ^\circ C ( 1317 ^\circ F)}\ [1 : 2]$



The determinants for melting points would generally also apply to the boiling points of ionic compounds. However, it should be noted that other factors would affect the boiling point as well.