Although Melissa is busy in real life, that doesn't mean Donna is gone from Chicago Fire forever. We've seen similar situations in other dramas, where a main character's spouse is shown less and less once he or she isn't really needed in major storylines. Take Bailey's first husband on Grey's Anatomy, for example.
As far as Chicago Fire is concerned, there will likely be plenty of opportunities for Melissa to reprise her role as Donna in the future.
Severide and Kidd's wedding is supposed to take place in Season 10 of Chicago Fire. Barring any disasters that might cancel their nuptials, there's a good chance that Melissa will be back in her role as Boden's wife for that momentous occasion.
One thing that's for sure is that fans are itching to see her again.
Watch Chicago Fire on Wednesdays at 9 p.m. EST on NBC.