what happened if a unit that chose with Shady Spectacles die

Yes — the equipped unit still dies as whatever it copied, and Shady Spectacles survives the death.

The copy effect lasts only "for as long as this is attached," so at the moment it dies the unit's rules text is the chosen unit's. That means any Deathknell or "when I die" ability on the copied card triggers as normal — a real card copy can even pay a cost like "recycle me" in the trash, while a token copy can't (FAQ #12489).

The gear doesn't die with it. When the Top-Most card leaves the board, the attached Equipment detaches and stays at the last location; since it's now an unattached non-Unit gear at a battlefield, it gets recalled to your base during the next cleanup (Rules 436.4.a, 459.1). The unit card ends up in the trash as its original self — the copy identity doesn't follow it there.