After the first 120 years, there are likely to be no biological parts left. Our cells can only divide so many times before they stop and die. Depression is largely a biological function, so I would not expect suicide to be an issue after the first 120 years.
Much of what makes us individuals is tied to our biological systems. If, for example, the section of my brain that is scarred from an injury were to be repaired with a perfect electronic replacement, the immediate change would be reinstatement of the ability to experience emotions normally, with the known side effects of improved social ability, better ability to prioritize and focus, and improved memory function. As long as I can get replacement part, I would expect no degradation of this facility over time.
Electronics are not affected by chemicals, so my replacement part would not be subject to fatigue, drugs, hormones, hypoxia, or any number of "environmental" issues that affect biological systems.
As the biological portions of the brain die and are replaced with electronic alternatives, things would change. Emotions are in large part governed hormonally. In my case, having just restored my ability to experience emotions through replacing a nerve connection with electronics, would I lose the ability to have emotions at all as the ability to create and metabolize hormones was lost with the biological systems?
Without an electronic analog to the endorphine system, the person would cease to have emotions. With the absence of emotions, they lose the ability to recognize or respond to normal social stimuli, have reduced ability to prioritize, focus, and remember information.
Human memory is incredibly compressed. We don't remember entire events, only the novel aspects of the events. We fill in the gaps between he "bookends" with reasonable speculation. After 17M years, unless their memory model is changed with a hardware upgrade, they will probably remember their first time at summer camp, but have compressed all other wilderness experiences into a single homogeneous blur. Now, with that said, once they have a certain amoung of electronic modification, it is possible that their memory model could be altered to incorporate mechanical augmentation such as capturing and restreaming experiences.
A number of people (@L. Dutch) have commented on the emotional toll of isolation as it applies to neurotypical humans. However, this person will no longer be neurotypical after a certain point - their neurons will all be replaced with electronics, and the endocrine system gone or replaced with electronic analogues. As one who does not experience normal emotions, I do not experience the effects of isolation in the same way as neurotypical people. I am more than satisfied in that regard by visiting a fast food drive through window once a day. I would expect the character would end up with a similar lack of interest in social interaction.