My understanding was that the menorah DID stay lit for 8 days, long enough for the HAshmonaim to acquire olives, get back, and press them for pure olive oil. The process took slightly over a week to accomplish, and the menorah never went out during that time.
And if we wonder why it is considered an 8 day and not 7 day miracle (After all, there WAS enough oil to burn for the first day), the miracle was that in the midst of that Churban and tumah, that ANY pure untouched oil was found at all!