I have a valley in my kitchen/family room roof join....and of course gutters....ice dams...but never had them tear off the gutters.
I think I need to install heat tape on the roof edge.....the roof is shallow pitch, sheltered from the wind and gets a build up os snow.....and because it faces west, it gets some winter sun which melts it a but....but then the sun moves and the ice refreezes. I have had ice cicles so big I couldn't open my back door....but so far no damage to the gutters.
Linda C

I would like to think that any gutter and down-spout man in your area could install gutters that wouldn't cause the problems you envision! If not, then hire another gutter-man! Or, move to Florida, or some other warmer place!