Early European Farmers displaced the mesolithic Hunter Gatherers in the areas they both inhabited but there wasn't a complete elimination of the HG groups. In fact, the I1 Y haplogroup associated with Germanic tribes comes from the mesolithic Hunter Gatherers, so they obviously were _not_ totally eliminated. Actually, it was the EEF group that was more or less fully eliminated in Scandinavia when the Yamnaya appeared because both groups exploited similar areas. They wanted loess soils along rivers, while the Hunter Gatherers lived near the coastline.
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However, the Corded Ware culture that largely displaced EEF in Europe itself had a large EEF component in addition to Yamnaya (and in some places like Sardinia EEF still dominates).
BTW, the only modern Indo-European ethnicities/language families that are not Corded Ware-derived are Greek, Albanian, and Armenian. (Indic and Iranic speakers resulted from a Corded Ware migration out of Central Europe back into the steppe, completing the circle begun with the Yamnaya migration out of the steppe into Europe.)
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