Kathy,

That is a good question. Trees are not immortal, and do eventually die. Ashes can live longer than 100 years (even close to 200), but that assumes a lot of things are going right. Boulevard trees have to deal with a lot of environmental stresses such as soil compaction, road salt, lack of space, and wounds from string trimmers/etc. Ashes are tougher than most, so not surprisingly people planted them there. Now we are paying for it with emerald ash borer (EAB).

What I hope the arborist did is something called a tree assessment, which can tell them the risk of the tree failing or dying. Here is a another template used by the Department of the Interior that is a little more intuitive. You'll notice that there is no "years until death", just a risk level/percentage.

If your tree is treated by injection (which is most effective) there is a small wound that is made every couple of years. There is a small risk that wound could be an entry point for decay, but not treating the tree would be a death sentence with how much EAB is out there in Carver County. Depending on the size of the tree other treatment techniques that do not drill into the wood---such as soil drenches---may not work well.

In some cases, I have seen people start to treat ash trees when they have already lost much of their leaf canopy (>33%). If it gets to that stage there is a much higher risk that the treatment would be ineffective and the tree would die. I do not know enough about your situation to see if that is what happened here.

Personally, I would get another opinion from a different arborist before I make any other decisions about what to do with the tree.

Best,

Shane