Neither the 180 day dispute window nor eBay's MBG will apply here.

If the item was mailed 31st October, then the purchase was made before eBay's MBG (introduced November 1st, and allows 30 days on top of the last ETA), as well as before PayPal's 180 day extension (applicable to purchases made on and after November 18).

As to how long... On another site's forum last night, there was a thread by a seller who had just received a message from a buyer saying that they didn't think they'd received their purchase......from 2011.

o_O