If the unions and employers don't reach an agreement soon German TU law means they have to enter a kind of arbitration phase, which would begin around the 6th April I think, and conclude by the 13th. Strikes are not allowed during this period. But if arbitration doesn't lead to an agreement there could hypothetically be more strikes after the 13th. (I have no idea if this is or isn't likely, just trying to give you as much of a picture as I can).
If the back up flights are genuinely fully refundable, then why not?