I think it is possible to write good scenes which consist entirely of dialogue, literally with nothing else, not even dialogue tags -- I sincerely hope so, anyway, as I have several in my WIP2. I've also got two "scenes" (one in each of my main WIPs) which each consist of one line of dialogue amounting to no more than a dozen words, so again I think it can be done, and can be effective.
But, and I'm afraid that it's a big but, I agree with ctg that they don't work here, RJM. Firstly, coming one after another like this, it's far too much, making the whole thing seem disjointed -- again, rapid, snapshot scenes can work in some contexts, but not, I think, here. Secondly, these are big important scenes, and writing them in this way short-changes the whole drama.
I didn't know about the having-to-abdicate thing, but I certainly understood what was happening because you put a giant info-dumping, drama-killing, explanation in there
He was not to know that the wine was a gift not from his trusted friends but from Eilderoess, his sworn enemy, who had infected it with the ceisorundra virus of madness.
I don't know why you chose to do it this way, but I think you would be far better off deleting that line, leaving his illness a mystery and then have the solution unfold in the course of two or three properly written scenes with plenty of action/drama/tension. As it is, there is no tension here, we're given no time to worry about him, and consequently we really don't care what happens.