Based off past park closures, they rarely open all at once and completely ramp up. Depending on bookings and such, I suspect they will do the same thing and only open 1-2 parks initially and possibly with limited experiences, then slowly ramp up, bringing back employees as the guests increase as well. This is the best financial strategy for any company, but especially a theme park. Just because they can open on June 1st, doesn't mean people will come back and if you are bleeding money paying for a fully staffed theme park, it will just cause more financial problems. And Disney does know how to run a business, even if we don't always like it.
And I think most people saw the furlough's coming, with the legislation for unemployment passing, it is much better for Disney to furlough everyone and allow them to collect the increased unemployment than to continue to pay staff that are not working.