So hypothetically speaking… how much life would you expect to get out of a fork? And how much would you expect to get out of a wheel/hub?

Years and years if properly made.
Mine:-
2002 zocchi DJ1 still perfect, 2005 Zocchi Z1 still perfect 2005 pike still perfect. All well used.

Hubs – hopes will last virtually for ever as they can have all wearing parts replaced. Other cartridge bearing hubs will be similar

much the same as above 2003 fox forks still spot on and no wear on the coating , they get used loads but do get looked after .

Hope bulbs must be 11 years old still going as is my ti-glide on the single speed.

But my ride buddy killed his fox forks in 14 mounths of no servicing

no replaced parts in any of my forks – not even seals

Had some Hope XC hubs since they 1st came out, about 3 bearing sets & 1 rear axle. No intention to change as yet.

(Pace forks have also been excellent without being serviced properly)

I'd say five years was a 'reasonable' life. Longer if looked after or not ridden hard, less if heavily ragged.