It depends GW hasn't really touched in the celestial lions in a while so right now they are either the entire chapter died out or they have recovered.The celestial lions are a chapter i really like since they are know for having a very strong sense of justice and value the lives of all imperials.This value of life lead them to arguments with the inquisition wich reacted my massacring part of thier chapter and later almost fishing them off in Armageddon as the Inquisition actually gave the orks information about were the space marines would be at.During this massacre many chapters were lost but 96 celestial lions were saved by the black Templars who sent them off into their homeworld to recover thier numbers or die with thier ancestors.I think GW could use this to create something like a rebellion between the Adeptus Astartes and the Inquisition.There is already a lot of tension between the astartes and the inquisition if the celestial lions recovered thier numbers and spread this information to other chapters along wiht other chapters coming out with the atrocities the inquisition has done am pretty sure they could get a rebellion going, not to mention that the Astartes would have public support since more people trust the astartes over the inquisition hell i bet that if the astartes would rebel the astra millitarium might join them as well.I think it would be awesome if the astartes came out and did something like this bringing a better time for the imperium not only would it be something refreshing but it would aslo get the plot going and they could bring back some primarchs to support thier chapters during this times as well as having the Alpha legion wich entire goal has always been to destroy chaos join the Astartes.At the end of the day the Emperor never wanted an organization like the inquisition to govern over his empire.Hell they cold even resurrect the Emperor, have the space marines discover the note that the grey knights safe keep and have them resurrect the emperor bringing a time of light for the imperium. But at the end of the day we all know GW wouldn't do something like that they would rather have an end of times 40k.