This is normal behavior in the swan world. If a male swan should lose its mate, it may or may not re-pair. This depends on the individual swan and species. However, usually, the male is just as content to go about its life alone. In the case of female swans, if something happens to their mate, they usually (again individual swan and species) will re-pair.

The other possibility is that your two swans are just around the bend in the immediate habitat that you cannot see and they have chosen to take up residence in the new area. This would explain why 2 birds are chasing the one. If they are the parents, they may be chasing this new swan from their old area, even though they may not be using it because they have found a better nesting, feeding and general living habitat. The Regal Swan