If you don’t buy it you will soon envy [a] the one who did [b].
If you don’t buy it you will soon envy [c] the one who does [d].
(The Cambridge Grammar of the English Language)
No doubt, [b] is anterior to [a]. But the relation between [c] and [d] is somewhat ambiguous (The book only says [d] is posterior to deictic time [speech time, I think]): [d] might be simultaneous with [c] or posterior to [c] or vice versa, I suspect. Which one is posterior to the other, or does it depend on the context?