I don't know how most women named Magdalene who live in England would pronounce this name. But I think that in the USA, almost everyone would find the "Maud-lyn" pronunciation to be eccentric. I've never heard the name pronounced without the "g" in the US.
However, there are several names which have different normal pronunciations in American English than the do in British English. Americans normally accent Bernard on the second syllable, while in England it's normally accented on the first. The same goes for Demi, which in the USA is normally said "deh-MEE" while in the UK people tend to rhyme it with Emmy. Neither of these is a "mispronunciation"; it's just a matter of dialect.
Pronunciations also do change historically. Just because Magdalene developed the pronunciation of "Maudlin" in medieval England doesn't mean that the modern English pronounce it that way. 21st century English is pronounced very differently from the way Chaucer pronounced it. Hopefully someone from the UK will clarify this. :)