A very unusual (I can't think of anything similar in any crime movie I have watched) scene occurs when Mike and his men in preparation for the replacement of Nacho's safe in a surprisingly patient and humane way (considering who they are) enter Nacho's apartment and Mike tells the two women that they absolutely must leave.
Mike is gruff but understanding -- it seems like he knows of them which implies that the Salamancas must also, they are no big secret -- and says, You need to go to your families; if you don't have family, go to friends; and if you don't have friends, makes some. But you must never return.
Part of this is that they have very important things to do that the women should not observe. But also, I think Mike is concerned somewhat for their safety if the Salamancas find them -- they would almost certainly torture them for what they might know.
But the problem is, they actually might know something -- there is the woman who has become psychotic through meth use and the other one whom has things more together and Nacho may, isolated as he is from anyone he can talk to, have told her things.
So Mike is relying on those women really leaving Albuquerque immediately and for good. This is best for them and essential for Gus. But safest for Gus would be to have them killed -- they don't seem reliable, they are dependent on Nacho and the amount of money looked to be between 5k and 10k -- not a lot. If they run out of money, they could well decide to haunt the old place, like stray dogs or cats who have been abandoned by their owners. Or just be found somewhere in the city, maybe the Salamancas have people with their photos at the bus station or airport.
Perhaps Mike made his, "They are not in the game" speech to Gus -- do we know anything more about why the two floozies were allowed to live, maybe from an interview with one of the actors or writers?