During delays, train drivers should announce metrobus options from the station where the train is. "We are currently experiencing delays because of a disabled train in Ballston. From our next stop, East Falls Church, you can take the following buses to other Metrorail stations: 2A to Ballston. Leaves in 3 minutes from Bay X. Art 55 to Rosslyn. Leaves in 7 minutes from Bay X. 3Y to McPherson Sq. Leaves in 9 minutes from Bay X. 2A to Dunn Loring, leaves in 13 minutes from Bay X. For direction to other locations, please check with the station manager."
This information could be read from an app like "Transit", or just passed onto a driver from metro central control. Cost should be minimal.