1) I’ll keep blogging, but it’s not really a way to keep in touch with people.
2) I’m on Discord, Instagram, Facebook and Tumblr. I prefer to keep my gaming of FB, Tumblr is kinda dying (and is also more of a blog platform than a social network), Instagram is just pictures, Discord is for chatter, not great for discussions. I have a twitter account but I never use it and I dislike the format (also not good for discussion), same for Mastodon.
3) No idea what fediverse or pillowfort are, but I’ve been eyeing MeWe. If people decide to migrate to one of those sites en-masse, I’ll probably follow.
4) I think creating a subreddit for the sg/g+/rpg diaspora might actually be one of the best possible solutions right now, if someone had the patience and willpower to set it up and maintain it.