There is no debt on good exchanges that offer crypto derivatives. Exchanges automatically close your positions when your margin balance nears zero. The best one - bitmex.com - has a 250 million insurance fund to cover the potential losses in case the price action becomes too volatile and there is not enough liquidity to close out everyone's positions in time.

Everything is seamless for the user, they don't even need know how leverage works, it's no different from trading on any other exchange.