In terms of durability, the switches are pretty similar, so as long as you stay away from LED backlighting, most will last a long time. As mentioned the keycap printing is the biggest longevity issue, unfortunately manufacturers love to charge a premium for decent caps. They charge an arm and a leg for a keyboard, knowing the caps will only last a fraction of the switch life they advertise.
Look into the non-backlit Ducky keyboards, they offer some with double shot ABS. The double shots will get shiny but never wear out. They can be found for about $130, however many places with them are currently sold out.
I would recomend a few things though, as mentioned before, CYA.
Before going whole hog, I would let your boss borrow one of your keyboards first and let him see if he feels it's worth it. Most feel the cost isn't really worth it, and considering how cheap you can buy normal keyboards these days, it may be hard for him to justify. Keyboards get spilled on, food dropped in them, and if the keys wear out, it's only $5 to replace. While mechanicals can be cleaned and repaired, it's not nearly as simple as just grabbing another $5 keyboard.
I would recommend against blue or buckle spring switches. I love buckled spring and they are the perfect office keyboard were it not for the noise. An office full of them could get quite noisy and some people are extremely sensitive to it. Remember, when they came out, they were phasing out typewriters, so they were actually quieter, that isn't the case anymore. Not only can it be hard to hear on the phone for everyone, many people have trouble hearing whenever there is lots of background noise. There is also what is known as noise aggression, which can make people go a bit nuts.
