More limited contact could have potentially alleviated some of the overall population loss from disease. If they only got 2 european diseases instead of a dozen, had it sweep through them, then had another 50 years before contact again, it may have made a big difference. It could have been possible to have multiple contact events over a 200 year periods to allow disease resistance to form without losing what may have been 90% of their population in one relatively large swoop.