If they were inseparable, this could only mean a couple of things, she was sick, attacked or picked up (rescued) by something or someone. We have seen swans separate for a couple of days. The only other explanation, is that the swan you are seeing is actually the female and the male went out for several reasons: He was chasing/attacking something or someone and got hurt or scared, he is not interested in nesting, he may have found another mate around the corner (yes this has happened), or again, something was wrong and he may have been rescued . We have heard of many rescues in the past few weeks due to flooding, fishing line, etc., so this is why we would suggest you check with the local RSPCA to see if an injured or sick swan was rescued in your area. Please let us know if the mate returns. The Regal Swan