This has two parts:
1) Is it okay to leave unused analog inputs on this device floating?
2) In the case where analog input exceeds the allowable range (i.e. Ain > Vdd + 0.3V, e.g. Vdd=2.5V, Ain= 3.0V), is it known how much current the device can sink before catastrophic damage occurs? The consequence of exceeding the limit is understood - we are trying to determine if this might be a source of errors we are seeing.