Less than you might think. Lots of older Eastern Bloc IR guided missiles have problems locking on to anything that doesn’t have the big thermal plume of a jet engine. They track exhaust heat and aren’t sensitive enough to ‘see’ the friction-warmed skin of an aircraft. That’s generally what these aircraft would be up against, so it’s not so high a threat.
Remember, our B-52s sweeping in at treetop height make dandy missile targets too. So do our AC-130 converted transport gunships. But they rarely get shot down by those missiles in that part of the world. This is another take on a concept we’ve used with great success - the converted transport gunship.
The Russians seem to like dual-role cargo plane concepts. That greenhouse ain't for growing flowers. (yeah, that's me:-)