You might try to reintroduce the cygnet, but it probably is not going to work and you need to be ready to recapture and save from its parents. If the cygnet is too weak or the parents just reject it for being away for so long, the ultimate outcome will be that the parents will try to kill it.

DO NOT give it to another pair of swans. They will immediately kill the cygnet.

Placing both young cygnets together on a secured lake is not an option. They both will succumb to predators as a 7 week old cygnet will still not be able to protect itself or the other swan.

The best option is to take both cygnets to a wildlife rehabilitator or waterfowl sanctuary. Raising both of the cygnets together will increase the chances that imprinting on humans will be minimal and they both can eventually be released as a pair on a private pond. The Regal Swan