I often prepare mini chocolate fruit puddings (in shot glasses), by combining fresh fruit and a melted truffle for guests; as a quick hors-d'oeuvre. I found a bulk package available, but they're short-dated to ~2 months from now, and it'd probably take 6 months to use all of them. Will my guests care/is there any downside to using the truffles as ingredient post-expiry?
I used to be quite fond of Lindt balls, and I was also a candy hoarder, so I ate many a Lindt ball past its "best by" date. If the Lindt ball has cracked, the filling will start to leak out and be unsightly. The leaked filling may have dried hard or crystalized, so the texture may not be good. If you have leaked filling on a Lindt ball, you can scrape a bit of it off with your fingernail for a taste test. They're usually fine to eat, though. Unless the package has been roughly handled, almost all the truffles should still in intact.
Undamaged Lindt balls a few months past their "best by" date are fine to eat. At worst, the chocolate shell will "bloom". Chocolate bloom is visually unappealing, and can have a waxy or crystalline texture which will may be noticeable on the tongue. However, it's still fine to eat.
The above mentioned issues are only cosmetic. When you melt the truffles, the cosmetic issues will probably disappear. This sounds like an excellent use for truffles that are slightly past their date.