How long can a dog go untreated?

Fleas can cause anemia, tape worms, among other things as well. If left untreated then yes they will get sick and die. Depending on where you live and how the cold the weather is, freezing weather can kill the fleas outside, however, not inside the house or on your pet. IMO you should not wait until it gets cold outside before the dog gets treated. You must treat the yard, the house and the pet in order to get the flea population under control. Treating just one will not get rid of them.

Fleas are parasites. In puppies and kittens, flea infestation can cause anemia. With adult dogs it can cause overall poor health and tapeworms. Not to mention terrible, constant discomfort. The dog should be treated ASAP. Frost does not kill fleas. It lengthens their life cycle (meaning it takes longer for the eggs to hatch, reach maturity and repeat the cycle), but it doesn't kill them. Not to mention, if the dog has brought fleas into the house the house will be infested as well. For every flea on the dog there are ten to twenty in the surrounding area.

i Would report those selfish Bastards

tell them treat it now, the poor dog must be so uncomfortable with all those itchy fleas biting him :(

if a dog or any pet is infested with fleas as badly as you say this one is, then he is going to be ill, with an infection and possibly parasites. Fleas mean ear mites, tapeworms etc, plus the poor dog will be scratching so much it will make itself raw and bloody leaving more openings for more infections.

They could get sick really fast. If they lose enough blood from the flea bites. They can develop anemia. And they can die from it pretty quickly unless they receive a blood transfusion. The good thing is that it is regenerative anemia which means their blood count is able to go back up to a normal number. But its really expensive to get this point. It should be treated asap, it is cheaper and they should not let it get to that point. I would treat the house no matter what. Then treat the dog with frontline plus, it kills fleas and flea eggs.

Fleas problem should treat immediately, otherwise will cause lots of health problems. And yes, if fleas problem left untreated, the worst case would be dealth.

Use flea control & treatment medication such as Frontline Plus or Advantage immediately.

You could use Vinegar to clear your house to kill any fleas too.

Yes, a dog must be cared for. Even when its a puppy. A vet must come in place in this situation.

Certainly fleas will make a dog sick, and if untreated they will most likely die. With that many fleas it would be best to take it to a vet, and have the dog washed and given meds. At the least, you could try using store bought meds.
And if this dog has been in the house, you then have a house infested with fleas. I would wash all linens with hot water, and wash all other clothes thoroughly, have all carpets and upholstored furniture shampood, and give the house a heavy duty cleaning. Do not wait till there's frost outside.