I'll give an example of my vehicle. It is Conqueror's Galleon a 2/10 with crew 4, but when it attacks it'll be exiled.
During your next untap phase it'll return as Conqueror's Foothold what happens to crewed creatures?
Crewed creatures are considered wholly separate from the vehicle themselves. They are not "on" the vehicle, and they don't share its fate in any regard or have any ongoing relationship with it. Crewing the vehicle merely means the creature gets tapped and has no further implications.
When a Vehicle is exiled then returned to the battlefield later, only that Vehicle is exiled, and only that Vehicle is later returend. The creatures that crewed it are not affected in any way, and won't be exiled in the first place. Similarly if the vehicle is destroyed or dies, this doesn't mean anything for the crew.
(Your Conqueror's Galleon gets exiled only at the end of combat, by the way, meaning it will do combat damage. It also returns to the battlefield transformed immediately, not at the next untap step.)
(Modern) magic cards use very precise language, and mean exactly what they say and nothing more. Crewing a vehicle means tapping one or more creatures, and apart from that the crew and the vehicle have nothing to do with one another.
If they were to be connected, the phrasing would've been more similar to that of equipments, explicitly stating that the crew is attached to the vehicle in some way.