They've let attractions remain offline before to save costs. Horizons was taken offline for quite a long time when it lost its sponsor in 94, reopened a bit later when several other Future World attractions were being redone. Of course it costs money and isn't good for maintenance in the long term if you have intentions to bring it back. But it happens. Disney has strayed far from a longterm thinking company, arguably the first huge signs of this were when maintenance budgets began being slashed during the latter half of the Eisner years and they started chasing short term profits and money scams like nextgen. Those practices are the norm and most certainly happen despite being stupid longterm ideas. They even do this when building new attractions, spreading the budget and construction time thin as possible over many fiscal years (as we're still seeing from the absurd length of time the Dwarf coaster is taking, and inevitably Avatar as well). Splash Mountain is already an extremely maintenance heavy attraction just based on its own show elements, the water only multiplies the issues an already complex and show-heavy ride has and it's pretty absurd to think that the bean counters running the company don't get excited at the prospect of not having to run the ride for as long as they can get by with. The attraction can be drained which i'm sure saves operational costs as well as maintenance when left sitting in a drained form for months at a time. Besides the money they don't have to spend on the water circulation, sensors, and powering all the lighting and animatronics and such, the show elements aren't being constantly exposed to running water splashing all over the place and causing mold or rot.
So really, think it through before being so shocked that this happens. It has before and it will again (especially now that they've got a $2.5 billion and rising disaster to cover up with nextgen, more budget cuts will end up happening). I'd be absolutely shocked beyond belief if the bean counters haven't objected to the ride's very existence and implore the company to permanently shut the thing down every chance they get. In the same manner that 20k Leagues, Imagination, World of Motion and Horizons were all given the chopping block due to being expensive to maintain (and either replaced by nothing or immensely less expensive to maintain rides instead). So no it's not a rumor that keeping a ride closed is something they would do to save money. Any ride that is heavy on show elements (especially those exposed to water throughout the day) is going to be expensive to keep maintained and running and thus raise eyebrows for bean counters who want to make cuts everywhere. Does it really come as a surprise and seem so unbelievable that they could have kept it closed on purpose for no other reason than to save money, after everything else Disney has done to the parks since the mid 90's to save cash?