I still reckon there is a chance Hamilton could move to Merc, there’s a few reasons.
Merc could (and reportedly have) offer him more money than McLaren, he would have a much freer choice over what sponsorship and endorsements he could do (so even more money).
McLaren are offering him a lower pay deal that what he’s currently on, as they have to pay for the Mercedes engines from next season. Another contract stipulation McLaren make is that they keep all trophies, which Hamilton has made a fuss about several times, and he’s trying to negotiate keeping the trophies into his contract, which McLaren aren’t having.
Hamilton consistently beat Rosberg throughout their junior years, so he would (probably) be No 1 driver.
His management company are XIX Entertainment, owned by Simon Fuller, they’re thinking past his F1 career too (hence having the ability to do more PR work important).
Final point, he doesn’t seem happy there anymore, I’m betting he’s had a falling out with the management.