Is it safe to eat expired hollandaise sauce mix
If it's a powdered mix, it's still powder (not clumped) and the pack is sealed, I'd go for it. Dried foods here are most likely to have a best before date, rather than a use by (real expiry) date. If it's clumped or the packet is damaged it may have absorbed water which wouldn't be good. It's possible that the flavour will have deteriorated a little. For example, powdered egg keeps for 5-10 years, most foods don't have longer than a nominal year on the label. 

A wet sauce mix may also keep that long if it's packed in a way equivalent to canning (i.e. sealed then cooked in the packet). 

If anything seems wrong about it, avoid it.