I was far from the only one that got a bad feeling when Blizzard confirmed Diablo IV will be an always online game last year, as many of us have lost a lot of progression and/or items because of power outages, a bad provider or something in games through the years. That's why I had to ask about this when I got the pleasure of talking with John Mueller and Joseph Piepiora, the art director and associate game director respectively. Piepiora's answer was fortunately a bit reassuring:
"There are reconnect-limits in place. I believe they are set at three minutes right now, so you can reconnect to the game you were disconnected from in its current form. But items that you have "lost" because of a disconnect are sent to your stash if they are of a certain quality. So let's say a legendary items drops on the ground and you have a random disconnect happen to no fault of your own and you're not able to reconnect for like five or ten minutes. When you reconnect, your game is over. The rare or magic items that were around will be missing at that point, but any legendary items will be back at your stash. The really valuable things won't be gone forever".
He also specified that items you pick up and collect will be saved the very second you pick them up, so stuff in your inventory will never be lost due to connection errors or something like that. The same applies to story progression and such.
It's a bit disappointing to hear the threshold for items being save is legendary, but it's also nice to know that we don't have to worry about losing progress or the best stuff in the upcoming very promising game because of minor server issues or problems on our own side.