Beyond the very good points that
@Fishmanic made, I would add that what you are proposing could become very time consuming. Please remember, before you start making demands on the mods, that we are volunteers, doing what we do as a service, and we have lives outside the forum. I myself tend to assume that the people on here are more or less grownups, and if they choose not to come around, that's their business. Unless they are personal friends or ask for my help, I don't see any reason to intrude on their decision.
As for the forum becoming extinct, that has indeed been a trend across the internet. I don't think moderators contacting members who have their own reasons for leaving would change that. However, so far this week I personally have approved the first posts of around ten new members, and I am only one of several mods. The fish forum in which I used to be involved died mostly because the admin abandoned it; this caused tech problems which over time caused most of the mods and active members to drift off, too. Neither of those things are happening here. I don't think we'll be going the way of the dodo bird in the immediate future.