Last I heard the union had voted to extend the agreement through the first week of November. This was not the first extension and will not be the last.
Florida laws do not mandate that eligible classes join the union. So, you've got many full time employees who are not part of the union. And, there are classes of employees who are not even eligible (seasonal, college program, executives, etc.)
In short, the likelihood of a strike at WDW is remote. The union could cause the company little financial harm, meanwhile Disney would simply start hiring more non-union staffers to fill their needs.
I don't know the details of negotiations (does anyone?) but I suspect as long as the union reps feel they are making SOME small amount of progress, they have nothing to gain by setting a strike date.