Generally, if a guy asks for it, and the service request is obviously "warranty type" work, rather than customer desires or customer damages, Ruger will send a shipping label, so you don't end up out of pocket for anything. Guys use middlemen, and I have had folks prefer to send through me many times over the years, even though I didn't do anything they couldn't have done themselves, but I've never understood why.
Front sights fall off; it's rare, but it happens. Whether it's caused by repeated impact hitting a perfectly soldered sight, or poor soldering by insufficient flux, insufficient solder, or insufficient heat, it does happen. Ship it back to the mother ship and mama Ruger will take care of it. I have a power custom front sight fixture, torches, and years of experience with silver soldering so I've done my own when I've shortened barrels or broken front sights - most folks don't.