I was thinking about the "only one Replicator survived" thing the other day. I thought it would be cool if they found a Replicator city under the sea, but it wouldn't be very logical, since they wouldn't have enough time or reasources to build one. Maybe several DID survive, but only the one managed to get somewhere. Perhaps a current or the turbine from ther sub caused it to get "sucked" into the sub. Thus they can't actually swim, it was a fluke that that one got inot the sub, all the others were trapped at the bottom of the ocean and eventually ran out of power and "died".