Work with any equipment for long enough and it will fail. Work in a venue without a proper PMS (and no, that is not referring to "Womens Troubles", but rather Preventative Maintenance System) and you will have problems. Even with a proper PMS, you should still expect problems.
Large shows which cannot afford to fail will often run tracking backup systems - basically they have 2 lighting desks, 2 FOH mixers, 2 foldback mixers etc. These systems will be kept fully synchronized with each other, and if one fails, the backup takes over.
As far as comms - a wired system will always be more reliable than a wireless system. Which is why you will find most shows will have wired to 90% of the people on comms, then wireless for those that really need it (ie Deck managers etc). They will also have a wired comms system sitting in the wings waiting, with a bloody long XLR.
Such is life.
Basically, you can plan a system which is almost impossible to have fail (full power backup yadda yadda yadda) provided you are willing to foot the cost.
Or, you can run a show in such a way that you can work around failures easily - ie I always run tracking backup of my lighting desk (when I have the facilities to do so), if I am TD of a show, I will always make sure that I have enough two way radios on site that they can be distributed if needed. I will always spec cue lights as well as cans, and I will always ensure that LX, Sound and Vision can run the shows from cue lights. If I am sound, I will always have two versions of my wireless mic sheet - the "All good" list and the "Make sure at least these people are mic'ed" list. Plan for the worst, hope for the best.