Is it permissible to go to a restaurant adjacent to the wedding venue where there will be impermissible (Sharia-violating) acts, and then leave with the family, or is it better not to go at all?

It is permissible to attend a feast that includes something objectionable if refraining from attending would cause significant hardship to the person, provided the attendance is symbolic, for congratulation and prayer, followed by a graceful departure. This is considered taking advantage of a concession when there is a need, which is what some scholars, such as Al-Subki, stipulated regarding the permissibility of adopting concessions from the statements of scholars when there is a pressing need, without habitually seeking out concessions.