Once you have exchanged contracts and completed on the house, you are obliged to vacate the premises on the date as mutually agreed through the Solicitors.
From that said date on; the house is the legal property of the purchaser, only if they wished to rent it back to you or give their permission.. would you have any right to stay at the property. Some people either back out of the sale or rent another place in this position, or alternatively stay at friends or relatives, whilst placing their possessions into storage until they find a permanent abode.