Of course the golden days are long gone. A lot of people, including me, left a long time ago.
I don't know how much pixelmon changed the server, but it seems like another reason the population is declining. I had a very good time on here, but at the end it just became boring. I have never missed the server after leaving. This was also after the "golden" days, which imo were the days when there were 30 people online most of the time.
The people that left were great and cant be replaced, but the server is not dead. I am NOT coming back, but if you want to "save" the server, you have to increase the amount of members. Since none of the old people are coming back you will have to get new people, though this will not feel the same as before, the generation of server members I belonged to is close to gone. Advertise on forums, idc, get new people, make them feel at home, make them get new people. Create a new generation.
Wipe mcstats if you have to, to encourage new people.
I mighht be wrong though, no idea, havent been here for months.