Until an expert can improve it, this will be a layman's answer. Since it would take longer to make a full circuit of the Sun, a year would include more days, and the seasons would be longer, IF the rate of rotation of the Earth stayed the same. Ditto on the layman's answer. I think that it depends on how much "slowing" we are talking about. If it slowed to a stop and then were left on its own, it would speed toward the sun, probably in something like a spiral trajectory, and would more than likely eventually crash in. If it slows, but not to the point of heading toward solar destruction, I think the orbit would degrade into a more eccentric ellipse and depending on the eccentricity of the orbit the earth may make itself vulnerable to a collision with Venus or Mars.