"Run dry" is simply a common term for losing oil pressure or volume. The MGB still has residual oil in it. When they tested the 139, it was run to operating temp, then the oil was dumped. Power was reduced to max endurance (the same thing the crew would do) and run well in excess of 30 minutes without any significant damage to the parts.
For those who want even better capability for extended "run dry" operation, the 139 now has an option for a configuration which is standard on the 189. An "emergency" reservoir on each side which will continue to provide minimal lubrication to the input module area (21,000 rpm) until they are empty. Pretty foolproof. No pumps or T-fittings required. That configuration increases the "run dry" time to 50 minutes. Proven in testing.