How to know about radical character of a diradical molecule?
Take a look at this is the article, which provides quantitative characterization of radical character:
M. Head-Gordon. Characterizing unpaired electrons from the one-particle density matrix. Chem. Phys. Lett., Vol. 372, Issues 3–4, 2003, p. 508-511

Based on natural orbitals, the analysis in this paper is applicable to any correlated method - it needs only one-particle state density matrix.