Warning signs of a bowel obstruction? Is severe constipation still able to be relieved after 3-4wks w/o a bm?

Normal bowel habits. In addition to seeing a doc for your impaction you need to be evaluated for other causes of bowel impaction. You might need a bowel regimen, colonoscopy and close momitoring until you get back to normal...A daily bowel movement.
Yes. If it is that long since the last bowel movement. It is advisable to seek help from your physician. Even with severe impaction, we have ways of clearing it out.
Where would poop go? Constipation is one of those things that a person cannot let go on for more than a few days, because the food he eats forms poop, and where would the poop go? There is no way to relieve constipation except to get the poop out. There are many ways to do that, depending on the condition of the poop, the patient, and the plans of his primary and gastrointestinal doctors. The poop must come out.