To my knowledge, you won't loose power because your energy provider forgot to buy energy from the market, they still have to pay for it though (probably with late fees).
It depends on the market design of course, but generally, if too many energy providers did not match their consumption with generation (or bought power), that could lead to power outages.
Concerning the 'late fees': if your consumption exceeds your production, you pay what is called balancing energy. Essentially, you have to buy the energy for a price that is set by the transmission system operator depending on the total imbalance in the grid. In some cases, this might actually be beneficial to the energy provider as the balancing energy is sometimes cheaper than the prices you get on the sport market close to gate closure.