I wrote a small console program for those who lost their history and want to restore it. It converts mContacts exported file in such a way that outgoing messages become incoming, and vice versa. So It's possible to restore your history from the history of the person you chatted with.
How it works:
1. Your buddy exports conversation history (between you and him) using mContacts plugin and sends the exported .dat file to you.
2. Make a backup of your miranda profile.
3. Run this conversation utility from the command-line specifying .dat file you received as the parameter, e.g.:
D:\mContactsSwapBuddies.exe "D:\Myst - Buddy.dat"
If there will be no errors, "D:\Myst - Buddy_swapped.dat" file will appear in the same folder.
4. Import history from this converted file using mContacts plugin.
If you are not satisfied with the result, you can restore your profile from the backup. For me it worked fine :)
5. ...And repeat the procedure for all your contacts :)
Here is the link: http://www.mediafire.com/?rwehyyzy4my
.Net framework 2.0 is needed to run this program.