The Disability Insurance Trust Fund finished the first quarter of 2015 with $54.3 billion in U.S. government bonds. This was down $5.9 billion from the end of 2014. The Disability Insurance Trust Fund had lost $6.4 billion in the first quarter of 2014.
There's no question that the Disability Insurance Trust Fund is doing somewhat better as time goes along. That's inevitable since the number of people drawing Social Security disability benefits is declining and the economy is growing. However, there's little doubt that the Disability Insurance Trust Fund will run out of money in the not too distant future. Because of the modest improvements in Trust Fund operations, I'd say that, absent some unexpected change, the exhaustion date is likely to be in the first half of 2017, perhaps around the end of the first quarter.
Benefits do not stop if the Disability Insurance Trust Fund runs of money. There would still be enough income to pay at least 80% of benefits. However, it would be a chaotic situation with benefits reduced by varying amounts each month since trust fund income varies significantly from month to month. Some older beneficiaries would be shifted into retirement benefits since they're entitled to whichever is higher. That would reduce the draw down on the Disability Insurance Trust Fund but be an accounting nightmare.