Even though already close, it will still be difficult for Democrats to pick up the seat, since the district has long been so Republican. But then, there's clearly Republican dissastisfaction, since Osoff is almost at 50%. if there's any more drop-off from Republican voters, that could push him over since he only seems to need to pick up about 2%. It's possible, but it will be hard.
Still, whatever happens in the June election, even if Republicans hold on to the seat, this should be troubling news to Republicans (regardless of what Trump tweeted about how forcing the run-off was a big win for the GOP). This was a very safe, deeply Red state for Republicans, and for a Democrat to end get around 47% of the vote (let alone at least 48% in the general election) shows a profound shift in voter attitudes towards the Trump GOP. It's less than ideal for Democrats to keep coming close, but losing, as they did the other week in Kansas, but one has to remember that these haven't just been Republican seats, but overwhelmingly safe seats, with margins in the last election of up to 30%. In fact, after the Kansas loss, Nate Silver on his 538.com site did an analysis and wrote that if that kind of voter shift held up in the 2018 elections -- even considering that Democrats lost the Kansas race -- it would mean Democrats could win 315 seats and control of the House. The Georgia race would seem to support that.