Two ways a sequel could be done:
Exact Copy
Ferris and Cameron work for a big company but it is too lovely a day to stay at work. Ferris takes for a day of fun. He tells the Hooters staff that it is Cameron's birthday, posing as wealthy investors they test drive the new Aston Martins, etc. At the meeting room the team leader says "Where are those specs, Ferris?", show his empty chair, a fellow worker (cameo by Kristy Swanson) says "My boyfriend's analyst's ex-wife said she saw Ferris passed out at TGIFridays last night." The weasly guy that wants the promotion that Ferris is getting keeps trying to catch Ferris. Everytime a co-worker tells him "Oh, you just missed him, he went to the mailroom (or other work related place)." Etc, etc.
Maudlin
Ferris calls Sloan and Cameron. They haven't seen each other in a while and he wants to have a day of with them. Ferris talks them all into skydiving (getting Cameron over his fear of heights), etc, et.
The night concludes with a really fine dinner. Ferris stands up, glass raised to salute the people that have been there during his happiest times. Ferris crumples during the end, he looks bad. "You'd better drive me home." he tells them.
His sister and parents are waiting for him at his house. "Where were you. You know the doctor said you shouldn't have too much excitement."
Ferris smiles through the pain, "I just needed one last good day."
Wolf