I would hazard the presumption that the plane became uncontrollable to the extent that the SatCom antenna software was no longer able to point the antenna
Inmarsat Aero-L used by ACARS makes use of a solid state antenna.
The "radiation" diagram of the antenna is omnidirectional (azimuth) and hemispheric (elevation).
Two satellites cover the area, one to the E (AOR-E sat), the other to the W.
As long as the antenna sees the sky the link is possible.