As of this post, there are 50 dead, 16 still missing. The volcano continues to put out dangerous gasses and ash. The 50 cm of ash built up on some slopes will contribute to a dangerous lahar when rains come. About a million tons of ash have fallen now--and it's a relatively small eruption.
Mount Ontake in calmer days
It's dangerous to hike on a volcano. Most eruptions have warning signs, but warnings can be misread...and worse, unheeded. This phreatic eruption--there was no warning for it. What could have saved people already up there enjoying their pleasant hike when the eruption came out of a lovely blue sky? Hard hats would have saved a few (though few of us want to go hiking in hard hats). A lightweight addition to your backpack is a dust mask--that might save you from deadly amounts of ash getting into your lungs and suffocating you. But nothing can save you once you're surrounded by toxic gas.
So be careful out there, hikers in the Cascades and Andes. Volcanoes are beautiful...but they can be deadly.