Annika,
If you read Bernie Brillsteins autobiography, Jim's manager and one of his closest confidents does indeed say that Jim more or less agreed terms to sell JHC lock, stock and barrel to Disney. Jim even bought out Bernies shares in JHC to be able to do it. The figure was 100-150 million dollars plus extra for Jim to stay on and supply his 'personal services' in creative areas. It goes into about 10 pages of detail on the deal and the daily events that surrounded it.
Jim wanted to get out from being the boss, and also wanted Disneys power and money to be able to move in the creative direction he wanted. He wanted to do a 3D movie and at the time that wasn't cheap, and most of the other things he planned were effects driven so he realised JHC would never be able to fund all that. So anyway it was very much Jim's wish to sell to Disney - he actually brought about the deal himself through his New York lawyers rather than through his manager.