What he told you was weird. I think you meant S02 (sulfite) and not S04 (gypsum), but neither kill yeast so he's wrong.
Sorbate and/or benzoate are used to prevent refermentation, and wine conditioner contains perservatives (those) so you can sweeten the wine/cider. There is sweetener in there too.
Sulfites (s02) are routinely used by winemakers. It doesn't inhibit fermentation at all, as wine yeast (and brewer's yeast) is very tolerant of it- that's why we can use it without stalling fermentation. It's used primarily as an antioxidant, as when it binds to the wine, it prevents oxygen being able to bind do it, as during racking. It also helps preserve the wine during storage/aging.
It will not carb up with the wine conditioner, no matter how long you leave it, if the wine conditioner did its work. Don't worry about it blowing up- it won't. You can keg, though, if you want to carbonate it. I wouldn't pour into the keg, as it could oxidize it, but you may not be able to rack it out of the bucket and into the keg without any problems.