I've often thought about doing the same thing (seeding a cereal into an existing clover field), but have just never done it. My expectation is that the rye will stay green and palatable well after the clover goes dormant this winter. Same in late winter/early Spring. Who knows, it may even help the clover. You'll just have to mow off (or spray dead) the rye at some point next Spring to allow the clover to grow without having to compete with the rye.