Apple is an industry leader for sure, and odds are they wont lose any money if the drop the 3.5 because apple is smart about the way they do things. Warrior is right, they will release a lightening to 3.5 connector for 50 to 80 dollars that will bridge the gap... however since it will be aimed at audiophiles, if they have a lick of sense they will likely do a higher quality DAC on it and advertise it as so. There are lots of blind apple followers out their though, and they are going to buy whatever apple puts out, with that there means there is a lot of money for 3rd party companies to make on apple products as well, so even if Apples does give the headphone jack the axe, there will be options...
The Mac book has one USB 3c connector, and one 3.5 headphone jack, apple is a minimalist company, I have no doubt the headphone jack will get the axe in this generation or the next, and they will be hailed and called revolutionary for it, it's going to happen.