The dried leaves will not rehydrate regardless of humidity level, and may fall off soon on their own. Alternatively, you can trim them off if you prefer. Their dried state indicates that the plant's roots got too dry or too wet at some point, though it's hard to say when; evergreens like this can have delayed symptoms of such damage since the leaves retain moisture for awhile even when the roots are stressed.

Feel the soil with a finger about an inch or two below the surface; if dry, soak the plant well so the roots can rehydrate. (If very dry, you may need to water it several times during the day in order to get it to soak up enough water, since bone-dry potting soil is difficult to re-wet. Use warm - but not hot - water to help.) If still wet or soggy, the roots may have already been too stressed from oxygen depravation and may have died back. In that case, the plant may be too weakened to recover and grow replacement roots, but only time will tell unless you opt to repot the plant and examine the roots by removing soil.

If the root system is ok, the plant might produce new leaves this winter, but it's more likely it will wait until spring. Don't try forcing it into growth with fertilizer; rather, it will just need to wait until our days lengthen to a point where it triggers growth. Keep monitoring it for soil moisture in that case, soaking the soil well when needed but avoiding watering when it hasn't dried out enough. Without leaves, it won't dry out often, but our dry indoor air will still slowly evaporate the soil's moisture in addition to the amount the roots use to keep the stems alive. Few houseplants do well with consistently-damp soil, but gardenia is particularly touchy about its roots staying too wet. When pots are kept on a saucer, make sure any water the saucer collects as drainage gets emptied right away so it doesn't over-saturate the soil by seeping back up through the drainage holes.

When new leaves do appear (or if you opt to start over with a new plant), place it directly in front of a window that receives sun at least a few hours a day. When too far from a window, not enough light will reach the plant to support photosynthesis and the plant may slowly starve. (Since light, not nutrients/fertilizer, sustains plants as "food.") Our eyes are not good judges of brightness indoors because they adjust so easily to changing light levels and conditions too dim for plant health. With winter sunlight levels being less intense than in summer, even a sunny window in winter is not as bright for a plant as we may think it is. Similarly, indoor ambient light from lamps or ceiling lights is much too dim to support photosynthesis unless those lamps are types specifically made as plant grow lights and used within a foot or so of the foliage. Although light level didn't directly cause this leaf crisping, it will be important to support the plant's recovery if it's able to regrow foliage.

Miri