I will start by saying that I would worry much more about YOU than about your boy. Yes, he will miss you, but he'll be just fine without nursing for a couple days. I say this from experience w/ traveling from my 18 month son who was at the same stage.
Ok now to YOU. You need to pump and I suggest pumping and dumping for convenience (flying with EBM is a pain, and not necessary for an older baby). You can probably get away with just doing it once about half way through.
Honestly, I would contact whoever is organizing the interview ahead of time (frequently this is an administrative assistant or some other sympathetic mom) and explain to them that you have a young child at home you're still nursing and that you'll need to take a break mid-day to pump. I have had tremendously good luck with this tactic - much better luck than just trying to covertly pump, which is the other obvious choice. The couple times I have asked about pumping I have had a nice room given to me and no questions asked (other than to see cute baby pictures). Then when I needed to pump i simply excused myself for 15 minutes and did what I needed to do. The times that I have just tried to grin and bear it I find myself hunting around for a suitable bathroom, sitting on the floor, and being annoyed.
As for the flight, I would just try and pump in the airport - there you'll be stuck with the bathroom stall and it sucks. When I did this I made sure I had my hand pump in case there was no electrical outlet (there wasn't).