The first thing you need to check when looking at gamut warning is what profile Photoshop is using to calculate the gamut. By default, that is usually whatever CMYK profile happens to be loaded. If that's what you are using, then you're not getting an accurate gamut warning. You need to make a custom preview using the output profile of the device you are print to, and even then, it's not necessarily all that accurate.
What kind of printer are you printing to? If it's a printer with a much larger than sRGB gamut then you're shooting yourself in the foot by using sRGB. If it's a chromogenic printer like Fuji or Chromira, etc, then sRGB is actually pretty close to the papers used in them.
"1. When you get a gamut warning in a dark spot of the image... does it just mean it will print as pure black?"
Not necessarily. It depends on how dark the area is, how much color is in that area and what the actual capabilities of the printer are in that area. On most printers, anything under about 12-15 RGB in the original file are going to print black.
"2. Does a gamut warning in a saturated color mean it shift color when it prints?"
Yes, it does, but how much it shifts and how visible it will be will depend on the image and the type of paper. What the gamut warning does not tell you, and what makes it a lot less useful than many people think, is just how far out of gamut an area is, just that it IS out of gamut. An are barely out of gamut and an area far out of gamut both show as simple "out of gamut." In the real world, you rarely notice areas that are slightly to moderately out of gamut. You also have the option of using Perceptual rendering intent to compress the colors rather than just clipping them. Or, you can do what I do in many images, convert a duplicate of the image with Perceptual and the original copy with Relative then paste the Perceptual into the Relative and mask to suit. Of course, you need to have the output profile and the lab needs to know that you have pre-converted.
"The reason I ask is that I did a soft proof using the adorama icc profiles on an unmodified jpg and noticed the lips went from a fuscia color to burgundy."
Fuscia to burgundy is a bit extreme, but chromogenic papers are notoriously limited in gamut, so it might be possible. Or it's just a crappy profile
" there a way to prevent the color shift and keep nice saturation? What is the best way to correct out of gamut areas without killing the saturation?"
If you've got severely out of gamut areas, you only have a few options. You can discard all out of gamut colors and print the in gamut colors "as is" using Relative Colorimetric. You can use Perceptual and let the tables in the profile move the out of gamut colors to the nearest in gamut color while at the same time moving the in gamut colors closer together to attempt to maintain the visual appearance of the original. The third thing you can do is to use a more complicated move using a copy of the channel with the best detail in it, duplicated, copied and pasted as a new channel with the blend mode changed to Luminosity, then masked to suit. That can put lost detail back into areas of high saturation and give the impression of higher saturation even though in reality it's lower.
One more thing you can do is use contrasting colors to trick the eye into thinking the colors are more saturated than they really are. This means things like making a blue more prominent next to a yellow, which make both of them seem brighter or more saturated. You get idea.