Because Lapsus$ monitors victims' internal communications, Microsoft recommends development of an out-of-band communication plan for incident responders "that is usable for multiple days while an investigation occurs."
My former employer has gone all-in with MS so they did not replace the ageing Cisco VoIP phone network that was sort-of independent, but mandated that Teams and other MS products be used for all internal communications. The issues of 999 calls was blustered away by saying everyone will have a phone.
Should be fun to hear the outcome when they eventually get hit!