Yeah that’s a popular speculation. It’s possible but there are other explanations. Warfare was common among the tribes and when a tribe lost they moved to other areas sometimes pretty far away.
But there is usually a tribe that moves into the conquered area and would tell what happened........
My understanding is the Indians that lived in what is now Plymouth, which they called Patuxet (http://www.tolatsga.org/wampa.html), were relatives of the Wampanoag Indians. Even Massasoit, chief of the Wampanoags, acknowledged Patuxet was wiped out by sickness.
Squanto, or Tisquantum (his actual name) was a member of the Patuxet tribe who had lived there, according to Captain John Smith, of the Jamestown Colony fame, in his book:
The generall historie of Virginia, New England & the Summer Isles: together with The true travels, adventures and observations, and A sea grammar
found here: https://archive.org/details/generallhistori00smitgoog