Well that's a bummer! I was looking forward to getting that (meeting the fab 5) checked off the list first thing when we got there!
I know! We have usually met Mickey and Goofy, although one year it was Goofy and Pluto. Also, the M&G doesn't open until the afternoon, I believe it's 1p, and it only goes until 7p. It is definitely worth going to, IMO. The line is usually pretty quick, the characters inside are a surprise, and you can stop at the photo shop on the way out of Epcot and they will print out a 5x7, for free.
You can meet Mickey, Goofy, and Minnie in the Epcot Character Spot and get a FP+ for it. They are not all together though, you meet them separately, but it is one line for all 3. Right across from that is Baymax (Big Hero 6) and Joy & Sadness (Inside Out). There is no FP+ for their lines, but we really enjoyed those M&G's and the lines were not that long. Donald is usually over in World Showcase, in Mexico, wearing his sombrero and poncho. The line over by Donald can get longish, but it moves pretty quick.
Pluto is usually out at the flagpole in MK in the mornings, and Donald, Goofy, Daisy, and Minnie are all in Storybook Circus (MK), although they are not in their regular outfits. One line for Goofy and Donald and a separate line for Daisy and Minnie. We have never waited too long here, I'm not sure a lot of people know they are there. In our experience, the Daisy/Minnie line is usually longer than the Goofy/Donald line. You can always check out kenny the pirate for more info. He is #1 in all character locations/times. Hope all this helps in your character hunt!! Have a wonderful trip!!