As an ex-hang-glider pilot...
Two other answers have covered the basic concept of gliding - namely that you're constantly descending, and to stay aloft you need to be in air that's rising faster than you're descending. Early hang gliders and paragliders had no problems staying up in normal ridge lift with glide ratios of 7ish:1. Before that, they were just an exercise in top-to-bottom "sled rides".
EDIT TO ADD EVIDENCE: According to Geoff Broom, the first hang-glider flown in Britain in 1971 had a glide ratio of about 3:1 in flat air, or 5:1 in ground effect from flying close to the hill, and this was strictly limited to top-to-bottom flights. By 1972, pilots on Broom's gliders were starting to manage sustained soaring flights in ridge lift. The Skyhook Mk3 hang-glider plans recommend learning on a hill with a 5:1 slope, requiring the glider to have at least this glide ratio or better.
In more exceptional weather conditions, of course, you can get away with worse glide ratio; in fact you may want to. Most hill pilots (myself included) have had the experience of the wind picking up during their flight and having to pull on full speed (essentially a dive) in order to get back down to the ground against the rising air. So it's theoretically possible for a wingsuit to stay up in those kind of conditions.
And in the most extreme cases, it may simply be impossible to get down. I've read of paraglider pilots caught in the updraft from a cumulonimbus formation, where they have literally pulled their canopy in around themselves and were still going up, because the cu-nim updraft was stronger than gravity.
What other answers haven't covered though is that you also need to be able to land. If you can't flare to a landing below running speed, then you have problems! Typically a hang-glider has a stall speed of 15-25mph, and from that speed can be flared to near-stationary on landing. A wingsuit flies at around 60mph, and cannot be flared in anything like the same way. A good wingsuit pilot probably could stay aloft on a ridge in high winds, but he'd need to pop a chute to land - and parachutes and high winds are not a healthy combination.