Yup, it was a Wreck-It Ralph version of the Pac-Man kill screen, complete with the Pac-Man version of Ralph running off with the cherries, as seen earlier in the film. Nothing really important, but one last little treat for the real old-school gamers in the audience. (Wikipedia actually has an entry on "kill screen," for those who are curious.)
As to the subject of a sequel (or prequel), I don't know the likelihood of getting one, but there are certainly a number of things they could still explore. One thing I was wondering about even before the movie came out was the identity of Fix-It Felix, Sr., and whether the the Fix-It Felix, Jr. game was meant to be a sequel in the way Donkey Kong, Jr. was a sequel to Donkey Kong. (If so, it suggests that Felix Sr. may have been the villain in his own game!) Although Felix Sr. didn't end up in the movie, the Buckner & Garcia song that plays over the credits does mention the fact that Felix Jr. got his magic hammer from his father -- a fact that I seem to recall hearing somewhere in the movie as well. So the seeds of at least one backstory/prequel are already there...
In any case, I'd also be happy if WDAS decided to produce a number of Wreck-It Ralph shorts in lieu of a follow-up feature film, the way Pixar has done with Toy Story and Cars/Mater, and Disney with Tangled Ever After.