I have no doubt he would've went along since the Enterprise was stolen from his facility.
I'm not quite so sure about that. Going after a starship in a shuttle sounds too insane for the real Mendez to even contemplate doing. But if Kirk is provided with an illusory Mendez who doesn't stop to contemplate, then Kirk (who also should have enough sense not to do something that stupid) could be fooled into acting against his own better judgement...
Do the Talosians have to consciously place the illusion in your mind or once begun is the illusion self perpetuating?
A very good question. A group of Talosians is shown "presiding" over Pike's illusions for great lengths of time, but are they doing that only in order to observe what is autonomously going on inside Pike's head?
Was it because the Talosians stopped projecting the illusion or was Pike able to end the illusion himself?
The abrupt endings all appear to take place at moments favorable to the aims and goals of the Talosians... Either Pike has just narrowly escaped death and could well be expected to enjoy a few moments of relaxing sex, or then the current scenario has failed to achieve its immediate goals and could just as well be dropped in favor of a better one. So we could argue the Talosians are doing the ending.
If Pike is going to live out his life on Talos IV does that mean some Talosian has to project the illusion into Pike's mind 24/7?
Supposedly, a major problem the Talosians were facing was the excessive use of their powers of illusion - on themselves. Projecting fantasies 24/7 might well be like breathing to them.
Mendez served the purpose of being a Starfleet authority to justify themselves to
A concern the Talosians might indeed have if they had carefully preplanned this all with Spock. They wouldn't even think of such things if they simply used Spock like a puppet in order to finally get their hands on Pike for good, or for some other natively Talosian goal.
Which raises the subsequent question of how Spock had come to reach an understanding with the Talosians. Who made the initiative? It would seem natural to assume it was Spock, as he'd plausibly care for Pike for Pike's sake, and he'd plausibly monitor Starfleet communications and be aware of the situation with Pike; the Talosians would not be likely to do either, not on their own, not based on what we saw in "The Cage".
Did Spock visit Talos a second time, then? On his own? By surrendering to the Talosians, he would risk little, as the aliens would have no matching breeding pair for a Vulcan male... But he could plausibly come carrying gifts, promising to deliver Pike to the Talosians; whether the aliens accepted this as a basis for bona fide negotiations, or took over Spock's mind and callously used him for getting Pike, Spock would get what he wanted.
Did Spock then perhaps smuggle a Talosian to SB11, to help manipulate Starfleet (as Phil Farrand half-jokingly suggests in his Nitpicker's Guide)? That would explain the Mendez illusion without suggesting the sort of interstellar telepathic powers that would ill match what we saw in "The Cage".
Timo Saloniemi