If you haven’t read Reamde yet, don’t click 
Where in the book is it established that Wallace was murdered? Zula is completely sure he is, but she can only infer it from a brief glimpse of a long wrapped-up package being carried out of the room, so it is a bit weird that she is so sure of it. And murdering Wallace seems unnecessary and too cold-bloded even for the thug that Ivanov is - there was no indication that Wallace was in any way disloyal.
I think it was inferred in the way you describe in your spoiler, and none of the other characters seem to think otherwise. Besides, Ivanov has pretty much gone off the deep end, and most of his decisions reflect this.
Also - [spoiler] from page 184 - the character Sokolev is going over the events that had occurred so far in his head, trying to figure out what’s going on, and it is brought up
I can"t think of anyone else that this could apply to except Wallace.[/spoiler]
I know - saw that - but it seems a really illogical step. Doesn’t make much sense. Is not really needed by the plot and the reaction of the characters to the event seems way too subdued.
I’m not done with book yet, but at one point, Zula is speculating that
Wallace was not really killed and this was all “gangster theater”. Then the automatic weapon fire breaks out.