Actually, suicide for Felix is not consistent with his character. Though he loves Sophie very much, she isn't his entire world. He has other options.
A more likely bad outcome for him is becoming like Brooks: a cynical, bitter, lonely, old man. (an outcome Brooks warned against).
Suicide is more likely for Sophie, especially if she loses everything: her career, her respectability, and Zack. It depends on how the Dev choose to portray Zack's reaction to her downfall. On the negative side, this isn't his first rodeo. He's broken up marriages before and targets married teachers. If he leaves as everything is crumbling around her, which he's done before (even alluding to this possible future for her the night she fucked him after coloring her hair red), that could be enough for her out of profound sorrow for everything she has lost .
That is not necessarily the bad end I see as most likely for her, however. A more likely dark end is she becomes a prostitute to make money, eventually gets hooked on drugs and alcohol to drown her pain and sorrow, and dies of a drug overdose similar to Dana Plato, the Different Strokes Actress.
