False premise. It wouldn't work. Even places that are small and isolated that supposedly "eliminated" the virus still have some cases (see, e.g., New Zealand), New Zealand is an island, so closing their borders is easy; they'll be hit harder, if anything, the moment they reopen their borders. They've already gotten dozens of cases from the few people they've let into the country from outside.
Hong Kong supposedly had eliminated the virus in June, and now they're locking back down with fears of uncontrolled spread.
https://news.yahoo.com/hong-kong-leader-says-coronavirus-critical-100-cases-085636893.html
But the city had impressive success in tackling the disease, all but ending local transmissions by late June.
However, in the last two weeks, infections have spiked once more and doctors fear the new outbreak is now spreading undetected in the densely packed territory of 7.5 million people.
On Sunday chief executive Carrie Lam said more than 500 infections had been confirmed in the last fortnight alone, nearly a third since the outbreak began.