Well planned fracture repairs heal reliably: the substantial majority of plated fractures unite without drama and return full function. The complications worth knowing are infection, implant loosening or failure before the bone unites, and non union, each uncommon, each fixable, each better caught early.
Send what your vet said and quoted. A veterinary surgeon reads it and comes back to you with what they can do and what it would cost, before you pay anything. A written second opinion is from $250.
Healing odds track with biology and mechanics: young beats old, closed beats open, simple beats shattered, and a well fixed bone beats a compromise. If your quote involves a compromise repair to save money, that can be perfectly legitimate, but ask what it does to the odds, and what the revision plan costs if it does not hold. Those two numbers turn a cheap option into an informed bet rather than a hopeful one.
Send the case, hear back from a surgeon with what they can do and what it costs, and only pay if you go ahead.
Not necessarily. Implants fail when healing is slower than the metal's endurance, and the cause may be biology, mechanics, an unlucky leap, or yes, occasionally technique. It is precisely the situation where an independent review of the before and after x-rays earns its fee.
Usually: antibiotics guided by culture, and a plan for the implants, which often must eventually come out because bacteria hide on metal. Frustrating, expensive, and almost always solvable. Push for a culture rather than rounds of guess the antibiotic.