I have used my Nashbar rack on a number of longish tours and it is still like new. It has done the Santa Fe Trail from Kansas City to Santa Fe, the Sierra Cascades route from San Diego to Reno, the Pacific Coast from Seattle to San Luis Obispo, and the Southern Tier from San Diego to Sarasota. In addition to that it has done a lots of around town duty, so probably at least 10k miles with a load and some without. It has been solid and never caused me the slightest concern.
I am not sure how much weight it will safely carry, but I have no concerns about carrying a light-ish load on it. That would include anything up to and including my full ultralight camping and cooking kit plus a couple days food and other consumables. That said if in doubt some weight can be moved to a bar bag, frame bag, bar roll, or even a back pack.
I have heard complaints that the bolts supplied with it for attachment at the canti bosses were inferior and prone to breakage, but I didn't use them so I won't comment on them. I find that the original bolts on the canti bosses are almost always long enough to accommodate the rack.
Even if it did fail, for the OP the worst that could happen would be that he would have to put his back pack on his back until other arrangements could be made.