It was a close run thing. Though of course diseases mean that the natives would be thinned.
Then again Vinland means that native American populations would be relatively more robust come the second wave of colonization.
Epidemology does not work that way, in an isolated Vinland seanario resistence would not be maintained and in an linked Vinland one the population would just be killed off earlier (and its a multi century recovery with the natives still at a disease disadvantage).