To the OP== your doing the right thing... re do it. 

Back to the OP, I thought that importing (not drag/drop, or launching via SONAR) a MIDI file stripped off the tempo information. Is that no longer true?

Yes Importing MIDI strips away the tempo data. This is mandatory and will never change.  It's the only way to plunk a midi clip in an existing song. Otherwise nothing would sync up.
 
But whole midi "songs" need to be "opened" to create a project with the correct data to have that song play correctly as compossed.

I have understood the problem as the following (am I wrong?): there is a MIDI clip which was recorded without click. So, MIDI file tempo is (constant) 100BPM while the content has fluctuating (not constant) BPM around 60.
 
The goal is to put correct (not constant) tempo into that MIDI file (from other view point that is setting correct for real tempo MBT in MIDI events). Then the file can be used in the project with real (for original MIDI) tempo map or in other project with different tempo.
 
The process has 2 steps:
a) find the original tempo. All (?) known methods require rendering the clip into audio first (if there is no other audio clip with exactly the same tempo, f.e. drums played live in parallel with the keyboard). Then applying manual or automatic (Melodyne) methods to extract the tempo.
b) once the tempo is extracted, the method in my previous post can be used to apply it (to the MIDI clip)