1. Why did the QAR lose the last 45 seconds of data?
This has been mentioned before. Apparently it's part of normal QAR ops. It's not a continuous recording system like the CVR and DFDR.
The recording system collates data and dumps it onto the QAR "tape"(PC memory card) at specified times.
Why didn't it complete the recording after the crash?
Nothing would have worked
after the crash (QAR, CVR or DFDR).