So sad. That is the one thing about biking I dislike- it puts you front and center with roadkill. A tiny little fawn, still with spots, that was killed on a regular bike route put me in a funk for days.
Our two cats go on leash. I started them young, but know others who started later in life. We use a cat walking jacket (google it) and they start crying when they see it, they are so excited- even when it has been packed away all winter. They do enjoy a trip outside, which seems mostly to be for grass eating, but they are pretty content indoors, too. A well placed bird feeder and toys seems to do the trick.