Freezing a dying person can definitely help: as the saying goes, "they're not dead until they're warm and dead". The problem is that this causes serious tissue damage (in the present at least).
If you just throw Bob into a vat of liquid nitrogen, water will freeze inside his cells and cause them to lyse. So you'll have to be a bit more careful. If he's frozen slowly, the water will leave the cells through osmosis as the ice forms, so you won't have that problem. However, this means you end up with a lot of ice in the space between cells. As this ice expands it will push the cells apart and cause damage to the structure of the tissue, and when the cells thaw they will have lost a lot of water. Also, most chemicals dissolved in the water will not be incorporated into the ice, so the concentration will increase as the amount of liquid water goes down. Not optimal.
A small number of animals can survive freezing by replacing some of the water in their body with cryoprotectant (antifreeze) chemicals: waterbears use trehalose, wood frogs use urea and glucose. If you fill Bob's body with cryoprotectants the water will vitrify instead of freezing as it gets colder, avoiding most of these problems. The difficulty now is that most cryoprotectants either don't go through cell membranes, or are toxic in high concentrations.
New cryoprotectants are always being developed, so it's not much of a stretch to assume we've found something less toxic by the time we're fighting full-on space battles. Bob's comrades could fill his bloodstream with our fictional new preservative, then freeze him very quickly in a tank of liquid nitrogen. The water in his body would go into a glassy state (hopefully) without causing further damage. Then when they got back to the hospital he could be revived and treated for his injuries. This probably wouldn't be very pleasant for Bob, since it would effectively kill him for a time, but at least he would get better in the end.
