If you look at figure 17 of the datasheet, you can see that with no heatsink, at temperatures up to about 40 degrees celsius, the device can safely dissipate about 1.5 watts of power.
Per table 3, collector-emitter saturation voltage is at most 1.4 volts at 1.25 amps. 1.5 watts divided by 1.25 volts is 1.2 amps.
If your individual outputs are drawing lower power - say, 500mA, table 3 tells us the forward voltage will be at most 1.1 volts, in which case you can sustain a total of ~1.36 amps.
Adding a heatsink can increase the maximum dissipation to as high as 4 watts, depending on the size of the heatsink, which would allow total currents as high as about 3.5 amps.
tl;dr: Without any heatsinking, you can more or less handle one pin at 1.2A, or more pins at lower current. With heatsinking, this limit is increased substantially.