Hmmm, Tron only had translites. If you're referring to the 3d translite be very careful since they're hard to come by (and not cheap).

May I recommend heating the front of the glass with a hair dryer as you seperate the two? Hopefully that will help reduce the chance of damaging the translite.

how bout a brushless vacuum attachment, holding it slightly away so as not to scratch?

I personally would take those dimensions to a local glass shop and have them cut and have tempered. Really though, unless shipping is outrageous, doesn't seem like too bad of a price.

For reference, I paid about $40 for a widebody playfield glass for my JD a couple years ago.

As for removing the broken glass. You might try using a spray bottle with soapy water. Could help loosen the glass and act as somewhat of a barrier on the front from abrasions (untested of course )

My original tron 3d translite was scratched, but it seems the backside is much more vulnerable.

Local glass shop is the way to go (under $20)
I would use a utility sink and rinse the translite in cold water.
The glass will wash off no issues.

I thought the glass would be tempered? Is that only playfield glass?

Back glass is not tempered or you would be vacuuming up a million pieces.