Well, here's my predicament. My wife and I are staying at the GF for our 5 year anniversary and I'm surprising her with an illuminations cruise so I'd really like to be able to walk back through Epcot to catch the monorail. But if we have to take the bus, so be it. My other question is what about people who park at Epcot and then do the cruise. How do they get back to their cars?
If you're doing an Illuminations Cruise, that my be a horse of a different color. Whatever nunber you called to get the cruise, you should call them to get the answer to your question. There may be some kind of special dispensation for people who are taking the Cruise. I'm sure that many people who do the cruise were originally visiting Epcot during the day. If you approach the main gate with a receipt proving you had an Illuminations Cruise, they might let you in.
Another option:
Don't drive to Epcot, take the monorail. After the cruise (which, ,according to allearsnet.com, departs from the Yacht Club Marina, walk over to Disney-MGM Studios, and take a bus back from there. Even if Epcot CMs DO you let you back in through International Gateway, it might be a shorter walk to The Studios at that point. The only concern is at what time did The Studios close? Buses run at least 2 hours after the parks close, so as long as they didn't close early, you'll be OK, and you'll only be on bus instead of transferring onto another, with a (somewhat) scenic walk along the way.
Another possible option:
Did you book the cruise yet, or are you still in the planning stages? If you're still planning, see if you can arrange to take the cruise on a day that Epcot has Extra Magic Hours at Night. Then you'll have no trouble getting back into Epcot, because it'll still be open to all Disney resort guests. The only caveat to this would be if you didn't go to Epcot at all that day, and your tickets don't have a park-hopper option. Then, you're potentially wasting a day just to walk through the parks. And if you've already gone to a different park that day, you can't get in at all.
And still yet another option:
Are you bringing or renting a car while at WDW? If so, you can make ADRs for a restaurant at an Epcot area resort, opt to pay for valet parking, and then time limits cease to be an issue. The only caveat to THAT option would be if this were the only day you planned to be at Epcot, and REALLY had your heart set on getting there and back via monorail.
And again still yet another option:
Drive your car to the MGM parking lot, and take the ferry over to Epcot from there. After the Cruise, walk to the Studios to get your car. Only caveat, like above, is if you were only going to Epcot that day and really wanted to go via monorail