Sorry you had this problem.
To be clear, the only real recording limit is disk space. Audacity could work with the 25 hour long 44100 Hz recording (albeit with corrupted values in Selection Toolbar) and would have safely exported your MP2 file. But this only applies while the overlong project is open. Once you close it, Audacity cannot open it again .
A theoretical, “possibly” least work method to recover the audio would be to split the project into three parts each of about 10000 AU files. However you need to know exactly what you are doing and I don’t know anyone who has actually done this. I’m documenting it in case any one wants to try it.
It means first making several copies of the AUP file as an insurance. Then select the first d00, d01 and so on folders until you have selected enough complete folders to contain about 10000 AU files (each folder should have 256 AU Files). Move all the other “d” folders out of that project.
Then go down the first copy of the AUP identifying exactly those 10000 AU file names (or whatever number it is). You may want to sort the AU files in the last complete folder by time so they are in similar order to that in the AUP.
Select and delete all the other file names in the AUP and terminate the AUP with the correct syntax (the same as it has now).
Then create a new project data folder, giving it a new name, with the same folder structure as the first project, “d” folders inside “e” folders. The “d” folders should contain the next 10000 AU files or so. The names of the “d” folders have to start from d00, as in the first project.
Take the next copy of the AUP. Give it the same name as the new project that has the second batch of 10000 files. Open the AUP and near the top, correct the _data folder to point to the name of the new project. Select from “<wavetrack name=” downwards all the file names that are already in the first AUP file and delete them. Identify the next 10000 or whatever AU file names that are in your next batch of folders. Then delete all the AU file names below that (again ending with the correct syntax).
Repeat for the final project.
The alternative method does not guarantee stereo channels will be correct - some blocks of audio will be in the left when they should be in the right. You don’t need the AUP file for this. Use Automator to sort the AU files by timestamp then rename them while time-sorted into a consistent alphanumerical sequence. Then recover the renamed files using the Intel version of the Audacity 1.2 recovery utility. You will want to work with a single folder each containing about 1000 (not 10000) AU files, so probably the AU files from four of the folders. 1000 AU files is as many as the utility can cope with error-free.
This process is explained at http://wiki.audacityteam.org/index.php?title=Crash_Recovery#Automatic_recovery_tools and you can download the 1.2 recovery utility from the link on that page.
At the end of this process (which does work with the noted stereo channel limitation, but assumes you did not edit the recorded audio) you will have about 30 WAV files which you can join together in Audacity ( see http://manual.audacityteam.org/o/man/faq_editing.html#join for how to join files).