can crypts survive as houseplants?

Yes, Cryptocoryne can be grown emersed in a room environment. However, their roots/rhizome should be kept wet and the leaves sprayed daily.

Yes, they seem to be able to grow as house plants, but they should be on a windowsill or some place where they get the kind of light that a house plant needs. I grow mine in covered jars or soda pop bottles, and so they get high humidities. I have not had experience growing them at the low humidities seen in the house, especially in winter.

Jan Bastmeijer has collected a number of accounts of crypts surviving in greenhouses when the heat failed and temperatures went down to freezing or slightly below. Therefore, they ought to survive in a pond in a winter where the lowest temperatures are only a few degrees below freezing. If you grow them in a pond in your backyard, make sure that they do not escape and become a new noxious weed in nearby waterways!

I have my crypt becketii, pointeriifolia, walkeri, willisi, balansae, tokinensis, nurii, graffithi happily living in my emersed crypt garden. They are living in one of my old storage box.

Just make sure that the substrate is damp, leaves sprayed with water at least once daily and if you are putting them in a makeshift greenhouse, spray them with water once a week.

Cheers
Vincent