There seems to be a consensus that bacteria do not get resistant to silver ions, so that would not be my big worry. A greater worry is that there is very little scientific knowledge about the long term effects on health and the exact mechanisms in vivo. Interestingly enough, nano and sub-nano silver are considered much more toxic than micron silver, so our quest to reduce particle size may result in a more effective antibiotic, but also increase toxicity.
There are many factors to consider if we talk about toxicity: Particle size, ionic or metallic, capped or uncapped... Also the way it is taken: orally, sublingual, topically. I don't believe much in "maintenance doses", I believe that is generally a marketing cue. I would rather take small, well directed doses, depending on the problem: skin rashes, ear infection to be treated topically, food poisoning orally (citrate capped nano silver has been shown to be more effective to reach the intestinal tract), cold and sinus infections using nasal spray and inhalation and generalized bacterial infections using sublingual.
As I believe that nano silver does not know to distinguish between good and bad bacteria, I would always recommend to take probiotics during prolonged oral use of nano silver.
I am not a MD, but I believe in common sense.