Is a person obligated to retrieve the satellite dish his mother gifted to his uncle, fearing that sins might be recorded against him if it is used for forbidden things, or is there no obligation on him, especially since his mother is aware of his desire to retrieve it and has promised to buy a replacement?

Prohibiting assistance in what is unlawful is conditioned upon knowing the state of the one being assisted, or by a strong presumption, according to some scholars. However, doubt or fear do not necessitate prohibition. It is permissible to sell juice to someone who makes wine if the seller does not know that. If you know that your uncle will use the dish for something unlawful, then it is not permissible for you to give it to him. However, if you have given it to him and the donee has taken possession of it, then you are not permitted to revoke the gift, and there is no sin upon you if he uses it for something unlawful thereafter.