Fate of Ecash if RSA is cracked?

Hello, After reading Comm. of ACM and Schneier's book about ecash, a question arose: what if the underlying public key cryptographic scheme gets broken somehow? Suppose, for example, that someone discovers an ultra-fast factoring algorithm or something like that. What would happen with all ecash that's been issued? Of course criminals would be able to forge large amounts of authentic-looking ecash, so banks should not be honoring requests to convert e-cash into real cash. I apologize in advance is this question is silly, and will appreciate your corrections. - Igor.