At this point -- if the parks do close -- I am guessing people will cancel vacations beyond that timeframe (for many many months or the rest of the year) --- With the amount of loss caused by closing the park for any amount of days, I would expect some serious cost-cutting when it opens back up -- reduced hours, construction halted, reduced capacity or rides being "seasonal" waiting for the crowds to come up.
Even thought is is 90 days away, I feel my vacation in mid-June is now in Jeopardy. (and that's okay, not complaining, just disappointing). Either my son's school will inevitably cancel classes and extend the school year .. or Disney may not be opened back up OR Disney just not in the shape I would want it to be in for a vacation.
My sister-in-law's family that was planning on going this weekend -- are now thinking of cancelling, especially if it doesn't cost them anything.