I have had clinical depression since I was 12 years old. I took Accutane at 29 with no ill-effects whatsoever, mental-wise. My mood actually improved as my skin cleared.
My doc said that there's a higher risk of depression for those who don't get their acne treated with Accutane when it's needed. He's not my derm, however, but my derm is also of the same opinion. As am I.
My depression was very severe. I was psychotic at one point. I took anti-depressant medication while I took Accutane and had slight liver enzyme elevations and triglyceride elevations due to both medications. But I do eat a healthier diet now than I did then, so I think my elevations would not be as bad now as then if I were to do Accutane again.
I had to stop Accutane as I injured my knee and then had to have surgery on it, so I did not finish the course. Stopping Accutane was not fun and I was not happy about that at all. It worked SO well for me and I still stayed clear for years after that one partial course.
The final decision is up to you. Did your derm know you have a clinical depression when s/he wrote the prescription? If so, then he/she did not think it was a huge risk, and really it is not as high a risk as the media hypes it to be. Monitor yourself very closely and also ask your friends and family to monitor you for signs of exacerbated depression. Then contact your doc for a possible increase of anti-depressant, or decrease of Accutane.
My doc also told me that a long term treatment, low dose, of Accutane is as effective as a shorter one with higher dosages as long as the cumulative dose meets what's recommended. He says those dosages are better for people like me.

My dermatologist (10 years ago) was not even a bit concerned about the depression as she knew skin problems can cause depression anyway.