There's never a good time to lose your best player to your greatest rivals, but there is a particularly bad time, and two days before a Champions League semi-final is up there with "while you're also about to lose your main striker" and "when said rivals are about to blaze miles ahead of you and dominate the league for a decade." So you see the problem Dortmund have here.
Real Madrid will have enjoyed last night's game, but it will also leave a considerable question: if Bayern Munich are capable of giving Barcelona the thrashing of a lifetime, shouldn't Real Madrid have built something slightly better-equipped at overpowering a team that can be so vulnerable
Mourinho's time is up at the end of the season, and he has not been able to deliver anything as convincing, euphoric or cathartic as last night's humiliation. He has been far from a failure, but the story remains the same: victory in the Champions League is essential, even more than it already was.
The sea change at Real Madrid may not be as severe or as demoralising as that of their opponents, but the loss of Mourinho, as seems likely, will be hugely significant. By the time these club take to Europe next season, things will be very different. The identity both have enjoyed in recent years will be gone, and replaced by something else. Dortmund will certainly be weakened, and so they will know that this season will be a case of now or never - while Mourinho will probably not be able to forego victory in this campaign because there may not be another. At least not in charge of this team.
What that means is that tonight is a suicide mission for both clubs - the last hurrah of two teams that, without European triumph, were good but not good enough - decent teams, stepping into the breach of the league when their rivals had off-years, but falling short of greatness. Destiny is at stake, and without a European triumph, Klopp's outfit will be remembered as also-rans, doing well to battle against a superior enemy. Mourinho's legacy may not be so kind - it may begin to look like a failure, by far the least impressive of his managerial roles so far.
Mario Gotze will be the main story, but his departure will probably give Dortmund fans something to get used to unless they can pull off something remarkable. Robert Lewandowsi will surely follow, and perhaps Marco Reus or Ilkay Gundogan the season after him. Tonight will be a chance, therefore, to make the party justify the inevitable hangover.
For the managers, there may be other prizes up for grabs - the chance to stake out a claim for a nice job in Paris perhaps, or even succeeding Sir Alex Ferguson. But it's the collective identity that will be lost, and how these two teams will be remembered that matter. In the wider picture, the demise of the two teams has been set in stone - but the chance to go out in a blaze of glory that could shape the future of them is a more worthy prize than the mere cup itself.