What to do with unused chip amp channel?
No, floating the op amps is not a good idea! Random noise can cause the op amp to oscillate between high and low at high frequencies if the inputs are left floating. Attaching the output to VCC or GND can cause excessive current draw and stress the op amp. Driving both inputs to high/low places stress on the amplifiers as well, as it will be driven as strongly as possible. 

You'll want to place the op amp in voltage follower mode, attaching the positive input to a divided voltage from VCC. 

Refer to this Maxim app note that explains very well how to minimize the impact of uncommitted op amps in your system: https://www.maximintegrated.com/en/app-notes/index.mvp/id/1957