Stef@n has posted a very clever approach over at http://chandoo.org/wp/2013/07/19/formula-challenge-001-return-everything-from-a-string-after-the-first-block-of-numbers-part-3/#comment-441204

He splits the string into progressively longer bits from the right hand side so he can find the start of that last batch of numbers, and then truncates the string from the left so that those numbers are excluded. He then searches for the position of the last number. Ingenious.

I’ve changed it so it doesn’t use whole column references, in case anyone wants to evaluate it bit by bit:

=MID(A1,LOOKUP(,-MID(9&LEFT(A1,LEN(A1)-(LEN(LOOKUP(,-RIGHT(A1&9,COLUMN(OFFSET(A1,,,,LEN(A1))))))-2)),COLUMN(OFFSET(A1,,,,LEN(A1))),1),COLUMN(OFFSET(A1,,,,LEN(A1)))),9^9)

He posted a shorter formula, but it doesn't work...I presume the wordpress parser ate some of it.