My vet said he's never lost a dog to HW treatment. Dutch was HW+, the shots kicked his butt, and yes you have to keep your dog calm and quiet for weeks. A friend has a Dane who went through the shots regimen years ago, her dog is just fine. The vast, vast majority of dogs who are treated for heartworms are absolutely fine afterwards.
With every medical procedure, there will be a chance (usually quite remote) of complications, including death.
Your alternatives? a: Do nothing, and watch your dog die slowly. Or b: follow one of the many "alternative" treatments touted all over the internet & take your chances. Personally I wouldn't trust most of those walnut hulls/supplement/voodoo whatever treatments when it comes to a life & death issue, but that's just my opinion. :)
There's a very vocal segment of the population who seem to regard just about anything a vet prescribes as evil and dangerous. To these people, the internet is Their Friend :) with tons of silly websites devoted to how dreadful medicine is, and how wonderful their "natural"
treatment is. Everyone chooses the best care they believe in for their dogs/families; it's your call.
I'd do the Ivermectin treatment, personally.