Based on my experience trying to navigate with OSM, if the Russians were using this to get to Kiev they would likely end up in Minsk before realizing they were off course.
Er, what is your source for saying "Russians using Open Street Map"? (I'm trying hard to make sure I'm getting good/accurate/verifiable information about all military claims -- and I can't find any more information about this online.)
There is no point. Data is mirrored in both raw ( .OSM.pbf) and processed form (i.e. OsmAnd, MAPS.ME map packages) all around the world (both current and historical data). You'd only draw attention to all the stuff.
At the end of the day, it's just a map. It seems like there'd be other ways to get maps if this one wasn't available.
I mean, theoretically the Ukraine's "IT Army" or Anonymous or someone could try to crack into Open Street Map and re-draw it so dead-end alleys are misidentified as major thoroughfares. (Or even renegade employees at Open Street Map.) But it also seems really hard to game out in my head just how much of an impact that would really have on any real-world outcomes.