There must also be grazing animals to serve both as prey and to fill the ecological void left by extinct herbivores. Horse and cattle flourished in late-Pleistocene and Holocene Europe, but became extinct in the wild there over the past 400 years as their habitat shrank. Both species still exist on that continent in domesticated forms and as escaped domesticated animals that have turned feral, and are already being used in local re-wilding projects. The Asiatic wild ass could also be introduced in Europe's drier regions as a proxy for the closely related, extinct European wild ass, which prospered well into the Holocene, possibly surviving in Spain as late as A.D. 1540.
Other large mammals could be used as stand-ins for closely related but extinct relatives, such as the Asiatic elephant for the straight-tusked elephant, which thrived in Europe's warm to cool temperate climates during the late Pleistocene. The Asiatic elephant could do well in Europe, because it is not an exclusively tropical species and, in fact, was widespread in temperate China early in the Holocene.
And let's not forget water-loving megafauna like the modern hippopotamus (which lived in warm, temperate conditions in Europe during the late Pleistocene) and the Asian water buffalo, which could serve as a proxy for its extinct European cousin. Finally, there's the Sumatran, or hairy rhinoceros, which, if saved from the brink of extinction in Southeast Asia, perhaps could substitute for the extinct Merck's rhinoceros, a related temperate forest species that became extinct during the last glacial period.