Dunno about Sentinels, if Offensive Bias is being redeployed to deal with The Endless then surely we won't be fighting Sentinels, unless Chief finds a way to make Offensive Bias his enemy, Lol.
Earth is 'safe' in the sense that it isn't destroyed but I don't know beyond that, Cortana only blew up Sydney but Lord Hood, Serin Osman and others fled Earth to another undisclosed planet, what that means for Earth, Idk, it may be weakly guarded right now with the UNSC scattered.
Also unknown if the AIs who sided with Cortana have surrendered or not and if all Guardians are deactivated.
Blue Team was sent off on a different mission by Lasky, shortly before the events of Halo Infinite.
Arbiter + Swords of Sanghelios are very likely busy defending their own planet, Arbiter had to retake his planet from Covenant splinter groups, likely still a few around but Jul Mdama's was the largest, then Cortana came along with Guardians.
Thank you for the explanation.