The current TiddlyMap codebase hasn't change much in the past months and no bugs related to a loss of data have come up so far. TiddlyMap always warns you when deleting content/tiddlers or relations between tiddlers so there is an extra safeguard against accidentally erasing content.
Another thing to mention is that I always try to make sure that every tiddlymap update is backwards-compatible with your existing data structure, so you do not lose any of your existing maps. If at one point an update were to be introduced that would break backwards-compatibility, I would of course highlight that.
So to sum it up: I am not aware of a risk of data loss related to TiddlyMap, yet, make sure to periodically backup your data and especially before doing any updates.
Best wishes
Felix