It all depends on exactly how stuff was entered into TMG and just what bells and whistles you used.
As you know, TMG's witness feature (one of its most powerful features) doesn't transfer by GEDCOM and I'm not really sure how direct imports of witnesses works into other programs.
I'd suggest trying a small dataset first using various options to see which gives you the best transfer before transferring your whole file. It will save you time in the long run. And as I've said, the people on the TMG mailing list can probably help with suggestions.
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