When Disneyland and Walt Disney World first announced they were closing as a precaution of the coronavirus outbreak, the plan was only to close through the end of March. Last Friday, however, that closure was extended. There is now no official end date for the closure, but there might be a clue as to when Disney Parks think things will be back to normal. Hotel reservations at the two resorts are blacked out, but only until June 1.
If you go to the Walt Disney World website right now, or for Disneyland, and try to book a room for anytime in April or May, the site will tell you that there are no rooms available. However, if you want to book a vacation for anytime from June 1 forward, the system will allow you to make that reservation. This would certainly seem to imply that the resort expects to be able to honor those reservations. The park has been refunding or rescheduling everybody who had reservations during the closure period.
Certainly, June seems like about as safe a bet as one can make under the circumstances. If the parks are truly closed until then, then they will have been closed for about 11 weeks when June 1 rolls around. Being closed for almost three months certainly seems like enough time for this to have reached some level of control. It might even be more than is necessary. The announcement that closed the parks until further notice does mention the possibility that the parks could be open earlier than June 1.
Honestly, if you were confident in the situation, and had the flexibility, if the parks did open before June 1, it might be the perfect time to go. With many people having cancelled reservations, and nobody currently able to make new ones, the parks will likely be as empty as they've ever been, especially if the parks are able to rev up and open with little warning.
Of course, the reverse is also possible. Walt Disney World and Disneyland are offering refunds to anybody with trips planned through June 30, so the parks are still hedging their bets regarding reopening. It's possible you could make a reservation in June right now, and still need to cancel it in a couple months.
Exactly what the parks will look like when all this is over is a big question. On the one hand, you can be sure a lot of people are going to want to return to normal as fast possible, and for many that will mean hitting Disneyland or Walt Disney World. At the same time, many might not have the means to do so due to the economic fallout. Disney Parks had a lot of new things planned, especially with the 50th Anniversary of Walt Disney World coming in 2021, and Avengers Campus at Disneyland Resort expected to open in July.