According to todays Mice Age Update the plan was to close the subs permanently Jan 4 while work was being done on StarWars Land. Stars Wars plan has been put on hold ,along with Fantasy land rides refurbishment, and Monstropolis has been dropped altogether. All this due to cost over runs and delays in Nextgen and MyMagic+.
http://micechat.com/49401-my-magic-plus-failure/ I edited my post to ad this link. Also, the subs run on batteries and batteries don`t last forever. Your iphone battery is only good for 300-500 charge cycles before it is reduced to 80%. Perhaps the sub batteries are at the end of their life and repacement cost is a factor.