I bought my car used and the top of the dash pad (full length) was already separated and raised upward. The lower portion over the pass airbag, above the
glove compartment, has also separated and curled upwards.

Finding a replacement instrument pad in the correct color is a project. Even if I can locate one, I can't really afford it.. or to pay someone
to replace it. So I'm living with it for now..

I did get an idea though. My windshield is a little crappy - no cracks or large chips, just permanent streaks and deposits from older wiper
blades. Visibility is good until I face a morning sunrise, then it all hazes up. My idea was to check out a new windshield and ask the installer to
let me at the front of my dash pad before they put the new glass in. I can pump some super adhesive in the gap and glue it back together. I'd lay
some 5lb weights on top until it set up. I have no idea how to approach the pass side (that folds over the top of the glove compartment) as it'*
nearly vertical - can't think of anything to press against it after I apply adhesive under it. Maybe just wedge something between it and the pass seat.

I don't carry full-coverage insurance, so the new glass will be out-of-pocket.. about $300 installed, with fees and taxes.

I haven't committed to this yet, it'* just an idea for now.

This is a 2001 LeSabre, right?

Sounds like a viable plan, just don't interfere with the air bag(*) in the process.

I haven't heard of this happening on one of these before. Any idea what caused this?

There is a YouTube video of a dash removal for the 2003 Le sabre, doesn't look too difficult. Once off, just reglue and add screws along the top edge of the dash for added measure. If the dash is too warped, locate one from the Pick and Pull junkyard about 25 to 30 dollars. To help clean the windshield try using 0000 steel wool pads.