Well not just the financial crisis, but as a result of a general US decline. I think English is very well suited to serve this purpose, being both fairly easy to learn the basics of, and with a very large vocabulary. However it’s not very old for that and seems closely tied to rising (& falling?) US power. Only 60 years or so has it been so widespread outside the native English speaking population. Before that in Denmark we’d use French or German and of course further back, Latin for science. And even further back there have been many other languages. Will English be able to hold on as lingua franca of the world despite falling US power?
And what would supplant it? Neither Chinese and Hindu would fit European language populations very well. Too different. Spanish perhaps, but the widespreadness of Spanish is not coupled with financial or military power. The same can be said for Arabic. French, German or Russian seems unlikely.