Going to the dance was not conditional upon getting housework done BEFORE you got sick, so darn it, being a consistent and strategic parent wins this time. So if it were me, the dance would remain unrelated to their lack of housekeeping, except "How will they smell on dance day?" would be their problem. But my mom always said "you never have to accept behavior that is unacceptable", so in my case we'd get the house clean whether the dance was on or not.
And beware the fatique and exhaustion of the flu! They may be dirty piggy kids, but your flu could make you seriously depressed about anything, including an overflowed garbage can! Once you're recovered, a week from now the housekeeping problem could feel like a much smaller issue.
Some way or another, unless their arms have fallen off, they have to clean up after themselves. Even then, there are assistive devices for armless homekeepers! I've been there, too. I always thought I could respect a mate who chose not to do dishes or laundry, but I'd find it hard to respect a guy who looked unable to. I dont want to marry a full time care recipient. I am a friend and lover, not a custodial caregiver. So I try to pass on the ability of self care to my kids. I fail a lot, but thats my goal = self sufficiency. Gosh darn it, my guys will be sorting their own #@$! socks before they leave my nest!