how many witnesses are owned or somewhat connected to Sun
I believe just 20 (currently the top 20). You can see which witnesses these are by looking at the witnesses @dev365 has voted for at https://steemd.com/@dev365. These sock-puppet witnesses are @car2001, @respect888, @paintingclub, @toke2049, @onestepaday, @bostonawesome, @nicetry001, @waitforyou1, @jumphigh, @flyingfly1, @aheadofslow, @happylife123, @hunger365, @cloudysun, @night11pm, @agirl10000, @coronashallgo, @high46, @eastooowest, @goodguy24
But can it become more decentralized if witnesses leave?
The community-elected witnesses will not leave. Either they will regain control by getting more votes, which has almost happened or there will be a community fork where users decide to adopt a version of the blockchain without Sun and the attackers.
RE: My resignation from Steemit