Reverse engineering mp3 to two tracks

So as mentioned in my other thread, I recorded a phone call with my bank today to have “proof” in case they pull more bulls*** with me!

The original recording captures from two channels onto two tracks. (Me and the bank rep.)

Audacity captured that as stereo, and I spilt it into two tracks. Adjust the panning so I didn’t get dizzy and saved it as two mono (?) tracks.

When I went to save it as an mp3, Audacity said it would save things as a mono track.

My question is, “Is there a way to create an mp3 or whatever format, and then have the ability to reverse engineer things so I would still have my voice on one track and the bank rep on another track if I needed to edit things after the fact?”

Of course I could keep the project indefinitely, but I don’t want to waste the space on a 30 minute call and file that is rather large.

Is there a way to “have my cake and eat it too”?

If it’s important audio-evidence don’t save in MP3 format as that’s lossy compression, which is an approximation.
Save an uncompressed format, i.e. WAV, or in a loss-less format like FLAC, which are exact copies.

If you adjusted the panning so there is some crossover : some left on right, & vice-versa, then the tracks are mixed permanently, no longer completely-isolated if you split them.

Step One for an important recording is Export the work as WAV (Microsoft) 16-bit and then move it to a safe place. Edit a copy.

Once you start adding effects and edit manipulations you could hit a condition you can’t reverse. Any mixing between the two tracks is permanent, and as above, never do production in MP3. MP3 works by adding cleverly disguised sound damage. The damage is permanent and can get worse.