I attend potluck gatherings regularly. If I bring something, I usually open it so everyone knows they can help themselves. There are rarely leftovers, but if there are, everyone usually asks before taking anything home. Yesterday I brought two boxes of tea bags to a gathering (it was a tea and cookies party) along with a batch of homemade cookies. By the end of the day, the cookies were all gone, and there was half a box of tea left of the ones I brought, which I took home after asking around. I also ended up trading different flavors of tea bags with other people, so we all ended up taking home different tea bags from the ones we brought. 
I almost always leave it. If I’m invited to someone’s home for a party, potluck, etc. it seems fair to leave them some leftovers to eat.
I’d leave it and next time, I wouldn’t bring as much. I’d also switch to whatever did get snarfed up because that’s what people want.
I notice that they did drink all of my damn beer, though… bastards.
In that exact situation, I’d leave it. If it had been a potluck and I’d baked or cooked something, I’d offer what I brought to the host, fully expecting and encouraging them to keep it. Depending on my relationship with the host, I might rummage around to find a container to leave my contribution in, and just take my bowl or plate home. When I bring food to someone’s home, I generally expect to leave it there.
Yesterday, I went to a potluck work event for which I’d baked zucchini bread. There was just a small amount left at the end, so I took it, knowing that my kids wanted it. I wasn’t paying close attention, but I think everyone took back their contributions. The event wasn’t at someone’s home, though. Had it been, I would have been more likely to leave the rest of the zucchini bread.
I would leave it, because the dip has now been sitting out for a couple of hours so I would just throw it away at home anyway, and I don’t need two bags of chips in the house. Plus, once I bring something, I consider it a gift, and it stays.
I was in that situation recently. We went to visit my wife’s family, and bought about 6 bags of chips with us. We opened 2-3 bags and put them in bowls, which were being munched on. The rest of the family showed up, and most brought 2-3 small items. There was a ridiculous amount of food there, all kinds of snacks, dips, cheese, sausage, etc. The rest of our chips weren’t opened, so when we left I asked my wife if we should take them with us, figuring she’d know her family’s protocols. She said yes, we grabbed our chips, said our goodbyes, and left.
If we’d have only brought two bags of chips, and there wasn’t so much other food there we’d probably have left them.
Coincidentally enough, I just watched “The Rye” episode of Seinfeld where George’s father takes back the rye bread and George (with Jerry’s help and a fishing pole) tries to return it. Great ep.