How can I reuse mirrored sliding closet doors?

Here's a post that might help you - https://www.hgtv.com/design/decorating/design-101/how-to-repurpose-mirrored-closet-doors

Put both behind a bed as a head board dress up like a window you could even stencil banes on the glass add curtains a vine around the mirror

https://www.pinterest.com/pin/25262447880397324/

I would buy table legs and turn it into a console or coffee table.

Have you thought about hanging them on the wall.

Hange them on the wall going up the stairs, or in a dark area you want to make more interesting.

Try this techinque. Find some interesting stencils and apply those with tape to the back side of the mirror and using a marker define the edges. Then take a dremel and remove the silver backing from this areas only. Apply some contrasting spray paint and when dry the effect is almost like creating your own piece of artwork.

They sell custom mirror frames, you could grab one and then hang the framed door or prop it against a wall for a full length, updated look.