Judging from the nutrition info in the link you posted I wouldn't be too worried.
It looks like the dextrose is just kind of a "carrier" substance for the reb A extract, which is likely because the extract is so sweet (about 300x sweeter than table sugar) that without some kind of filler the packet would contain like 10 little crystals lol.
Since it's listed as <1g sugars, you're looking at approximately somewhere between 0.5 to 0.9 grams dextrose (typical priming sugar) per gram of PureVia you added.
How much did you add to how much cider? Unless you added like 100 packets I wouldn't be worried at all. A typical carbonation charge for a fairly fizzy cider at 3 volumes for 5 gallons would be on the order of 200g of dextrose. Add to that the fact that bottles should be able to survive more than that and I'm pretty confident you'll be OK. Bottles may be a bit more fizzy than typical but probably won't explode.
As a side note it seems kinda skeezy to call this a "calorie free sweetener", since really it's more like a "very low calorie sweetener." I guess it's not so bad though, even assuming it contains .9g of dextrose per pack you're only looking at like 3.6 calories per pack lol.