I've accidentally opened loaded cameras a couple of times. I've typically completely lost about 3-4 shots in each case, with damage to another 2-3 shots and the rest of the roll being unaffected (except for some fogging around the sprocket holes). The details will vary with how long the camera back was open, how bright it was, and how fast the film was, of course.
I once had film rip in the camera as you describe, at a time before I began doing my own processing. Fortunately, I had a reloadable plastic film cartridge on hand. I was able to go into a darkened bathroom and spool the film from the camera onto the reloadable cartridge. My local CVS was then able to process the film, so even a minilab with a minimum-wage teenager running the equipment can handle this sort of thing. (I don't know if they'd be able to handle it loaded into the sort of plastic container that holds 35mm film, though.)
Worst-case scenario, if you can't find help locally, if you can get the film in the mail in a lightproof container, I'd be willing to process it to negatives for you. (I do my own C-41.) PM me if this becomes necessary.