Most have been preserved for a while. The last SW-1 in regular service was the 1849 (ex-B&M 1113) in 2014/2015. Berkshire Scenic Railroad Museum (BRSM) acquired the unit (ex-B&M 113) in late 2018; and is in the process of restoring the unit to original / operating conditions.
Link to BSRM 1113 site: