I didn't see anyone reply to this, so if you're still looking for the answer, yes, if you have 8 villagers the game will give you a random 9th even if you never go online. Sometimes it takes a few days, I've heard of people that went with 8 for more than 10 days. But someday the 9th will come for sure. If you don't want to start everyday plot resetting so their house doesn't ruin everything (it's a pain...), I'd advise you to quickly adopt a 9th villager, at least this way you can choose who they are and where they'll go, since you'll know when to plot reset.