Does anything flow out of an op-amp?
Both Martin and immibis have it correct. Here's a slightly more complete circuit, showing how I1 is absorbed by the op-amp output, then flows to the op-amps' negative supply voltage (the op-amp's positive supply voltage is not shown, but is still required).
You cannot accurately measure I1 at the -ve power supply, because there is additional quiescent current to bias the op-amp's internal transistors.