I don't know what would make your buds rot like that, maybe you could ask on the roses forum if nobody helps you here. But it is normal in our cold zones for rose bushes to freeze back to the ground in the winter. All mine do and they grow back quickly each spring.

Sounds like thrips...It is an insects that preys on roses. They are almost microscopic insects whose larvae bore into the unopened rose flower, damaged the petals and lapped up the juices. They make a roses have brown-stained petals, water marked petals, or one with holes in it. You will need to controll them by spraying with systemic insecticide. Hope this helps.

Botrytis blight, also called gray mold, a fungus disease that spreads in moist air and cool temperatures.

If symptoms appear again this year, cut off and destroy all infected plant parts. Spray with a rose fungicide to keep the disease from spreading, don't crowd plants, give good air circulation, water in the mornings and use soaker hoses so that you don't get water droplets left on the rose.

There are also many hardy roses that are disease resistant if you want to replace it.