Butterfly Fish Died

I just got a couple of butterfly fish and one did not survive the trip.

I got the butterfly fish all at the same time, to lower aggression, but now one has died. Can I add more butterfly fish later in life? Or is it more like a do it once thing?

Tank : 125 gal, with 55 gal sump, with coral beauty, two mocha clown fish, double saddle back butterfly fish, latticed butterfly, pearl scale, and banded butterfly and a spooted dragonet