Board Thread:Questions and Answers/@comment-30488984-20180630192929/@comment-25684606-20180630205451

It's often described that Daemons are incredibly resistant to regular weapons (I don't know how far that is represented in the actual tabletop) and that the Nemesis-Psi Weapons of the GK are the most effective against them. Since they can emerge from the Warp, so basically everywhere, I wouldn't count on artillery and since they wield Daemon Weapons by default, armor may be of limited effectiveness as well.

Given the fact that the knowledge about the true nature of Chaos is actively suppressed by the Ordo Malleus it's likely to assume that many Astartes' won't know too much about how to battle Daemons in the first place, so I'd say their chances of victory are pretty limited, but they might survive long enough to call for reinforcements.