I was returning to the "new" bar from the X-7 labs, and passing near the old church I discovered a Freedom who quickly shot dead another stalker... I killed the Freedom, looted the bodies and walked away - just as usual.
At the bar I talk to Voronin and he instructs me to meet Guide near the old church... and this make me think "no, it can't be". I reach the green target on the minimap and I find that the stalker was Guide.
So, I can go forward with the quest without talking to him?
Or I have to reload a previous savegame? I presume that the Freedom that killed Guide has spawned when I exited the labs, so I should take a savegame created while I was still underground.