So it takes 8 to 12 years for a human body to decompose into a skeleton.
So honestly, if the group can last 12 years, then they just need to worry about new Walkers then the outbreak Walkers. If 90% of the human race was wiped out in the first year, then walkers are a minimal threat in 12 years.
Give it a decade after that, with most of the survivors understanding how they need to handle humans that die, then the birthrate will allow humans to outnumber the walkers.
So honestly, if the group can last 12 years, then they just need to worry about new Walkers then the outbreak Walkers. If 90% of the human race was wiped out in the first year, then walkers are a minimal threat in 12 years.
Give it a decade after that, with most of the survivors understanding how they need to handle humans that die, then the birthrate will allow humans to outnumber the walkers.