The forward speed of a wingsuit flyer in steady state descent ranges from 100 mph to as much as 130 mph, depending on the specifications of the suit (membrane area and flier weight are the most critical). Given approximately a 4:1 glide ratio, that means a minimum descent rate of between 25 and 35 mph (= ~2200 to over 3000 ft/min).
Even neglecting forward speed, impact with a solid surface at that speed will be above 90% fatal; either chest trauma or head trauma can do the job.
A good flare can reduce this descent rate by more than half, perhaps even to near zero if excess forward speed is carried, but then the "landing" becomes a slide at speeds normally only seen when a motorcyle road racer comes off his bike. Those racers often survive with only minor injuries, however; I'd have do say, on that basis, that it's probably possible for an experienced wingsuit flier to land, if not safely, at least survivably on smooth asphalt or concrete (water is less desirable as this would then be equivalent to a speed water skier falling at above 100 mph).
The big issue here is that it's impossible to practice this kind of maneuver -- your first landing is the first time you'd try to land, and unlike when learning to fly an aircraft (or even a glider) you don't have an instructor aboard to coach you and take the controls if necessary, nor the ability to "go around" if the landing doesn't look right. By the time you're close enough to tell if it's good or not, you're fully committed.
It's worth adding here that wearing a full face helmet and hard body armor on chest, abdomen, groin, thighs, knees and shins, plus reinforced boots with steel/composite safety toes and ankle support would greatly reduce the possibility of broken bones and life-threatening levels of abrasion and laceration from high speed ground contact. This would be effectively the front half of what a motorcycle road racer wears (if you do this right, your back won't ever touch the ground).