Complex sentence: A temporary export ban would offer the National Galleries of Scotland time to raise equivalent money to save the painting for a public collection; however, this will not happen if it is sold to a private collector in the UK.
Split into simpler sentences: A temporary export ban would have offered the National Galleries of Scotland time to raise equivalent money to save the painting for a public collection. However, this would not happen if it was sold to a private collector in the UK.