Plant - Another band with success, not as big a success as Led Zep, but still big or becoming one of those singers that isn´t famous but people start recognising him on youtube and saying stuff like: "How did this guy go unnoticed???"
Page - Probably starts another band after The Yardbirds. Maybe with Steve Marriott? Imo that band wouldve been bigger than Humble Pie but Peter Framptons career would not be as successful and he gets stuck in the teen idol image as he got with The Herd
Jones - Session bass player, keyboardist and producer in the future. Can see him working with Jimmy Page maybe.
Bonham - Probably alive. Forms / joins a lot of different bands, bit like Carmice Appice.