Unique servicing question.

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The movement will never be new again, but parts with too much wear will be replaced and after a good clean and new oil the watch that ran for 20 years will keep just as good time as the new one. I recently serviced my old Omega which had water damage and kept very poor time, sure the movement doesn't look new but it keeps great time, within COSC rating. And that thing is almost 50 years old.
If a movement gets serviced every 5-10 years it should last way more than a lifetime.

Oh and yes, enough money can get you a new movement, but why would you even want that.