If Youngkin wins, I don't think it means that Virginia is becoming a purple state in federal elections again. Candidates can and do win governorships in states that are otherwise hostile to their party.
It'll be similar to Maryland in 2014, where Hogan won because of a favorable national environment, a strong campaign on his part and a lazy campaign by his opponent.
A key feature of Republicans gubernatorial candidates winning in safe blue states or Democratic ones winning in safe red states is that the result of the gubernatorial contest is usually a clear exception among the statewide and legislature races that cycle. All of the other statewide elections and state legislative contests are usually still landslide-level blowouts for the dominant party (see MA or MD in 2018, LA or KY in 2019).
Right now, the polls are suggesting that the Lt. Gov and AG races in VA are also very close, and control of the general assembly is essentially a tossup. These are not signs that VA has become a safe blue state.