Pump as much as you can and hopefully you have a store of breastmilk in your freezer that will last at least the next two days. Feed him that milk. You won't be "rejecting" him in any way at all, so stop that business right now. If you're anxious about bottle feeding him, he'll feel it, and stress is really bad for your supply.
Depending on what medications you'll be on following the surgery and what foods you eat, and how hydrated you can remain, you have a good chance at maintaining your supply. It will probably drop off but you can probably build it back up with some hard work. You can also get the help from an LLL.