<< It would be really nice if someone who has replaced a MIDI track with a RT in previous versions of BiaB would chime in, however maybe that person doesn't exist. >>

I've done this for years and using Note's test, RealTracks performed normally on my system.

<< In both of my tests the RTs did play and they played exactly what was shown in notation. BUT like you proved the audio tracks so not show in the tracks view. That happened in both of my tests. IMHO that is a major bug. >>

This is correct, but not quite. The RT's play but not the original imported midi data. The RT does not read and sound the imported midi. Generating the RT creates new midi data and that is what's being played and displayed in notation or the piano roll.
The audio and midi is new midi data and will change and update with regeneration or partial regeneration.

To prompt a RT to play the original midi data that was imported from a midi song file requires using the Playable RealTracks Feature. A SuperMidi track also can sound out the original data but I encountered issues closing the file and also had to manually display the tracks as they were hidden once the SuperMidi instrument loaded.

A special note to Notes (and Mario and others):
The Playable RealTracks concept was introduced in BIAB with a video tutorial in 2011 and updated to include user made UserTracks in 2014 along with the introduction of the Artist Performance File, a variation of a UserTrack but is proprietary to BIAB. This allowed RealTrack and audio editing in BIAB at the same level of midi editing.

I called these custom tracks "Combination Tracks" before Playable RealTracks was introduced in 2022. You may want to consider a deeper dive into this advanced, long time feature that's been virtually overlooked. I have a YouTube video posted in early 2018 of a cover of the Doobie Brothers "Listen to the Music" where a RealTrack modified to feature their signature acoustic guitar lick if you or others want to check a conceptual "Combination Track" out.
Listen to the Music BIAB Combination Track

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Midi Render.jpg (163.31 KB, 53 downloads)
RT loaded no generation.jpg (159.5 KB, 53 downloads)
RT generated New Midi Data.jpg (165.53 KB, 53 downloads)
SuperMidi plays original midi data.jpg (171.41 KB, 53 downloads)
BIAB 2025:RB 2025, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.