Without the Fregat upper stage, Grunt cannot travel to Phobos, yet if this powerful and massive stage were jettisoned, some less powerful, but functional, engines would be available for burns.

MSN: Salvaging Science from Stricken Mars Moon Probe: A Scientist's View - Technology & science - Space - Space.com | NBC News

Or, it could mean that they gain control of the spacecraft, but that the Fregat engine still will not ignite, yet the much less powerful propulsion units designed to land the craft on Phobos and propel the return capsule back to Earth are working fine.

MSN: Salvaging Science from Stricken Mars Moon Probe: A Scientist's View - Technology & science - Space - Space.com | NBC News