Staying on the island
The simplest option: guests fly home, and the two of you stay on for a few extra days at a quieter corner of Mallorca, often the Tramuntana coast, once the wedding logistics are behind you. Several venues offer better rates once the event itself has wrapped.
Island-hopping the Balearics
A short ferry or quick flight connects Mallorca to Menorca or Ibiza, each with a distinctly different character, Menorca quieter and less developed, Ibiza more social. A few days on a second island makes for an easy honeymoon extension without another long-haul flight.
Going further into Europe
Since you're already in Spain, a few days in Barcelona, or a short flight to Italy, Portugal, or the French Riviera, extends the trip without adding transatlantic travel time. Many couples treat the wedding week as the first half of a longer European trip rather than a standalone visit.