Can the non-stick coating be removed from cookware and still be useable?
Removing it mechanically (sanding with waterproof P100 and then again P200, steel sponge, sand blasting, ...) will remove the coating and expose the pure shiny Aluminium.
The advantages of Aluminium are :

light
cheap
conducts heat well.

The disadvantage of Aluminium is that it's a health risk if used improperly, so:

Let it oxidise for a few weeks after you've removed the coating so that it becomes dull again: Al2O3 is much harder than Al and has less risk of leaching into your food.
Use a lot of fat (oil, butter, ...) when using the baking sheet in the future
Clean it with soft materials (sponge, cloth, ...)
If it needs a thorough cleaning, you'll see the soapy water becoming grey: that's the Al2O3 being removed, so let it oxidise again for a few weeks.

If you take above precautions, you'll get another 25 years of usage out of it without it becoming a health risk!
:-)