Yes, if one of your tomato plants dies, it’s a good idea to remove it from the garden. While it seems like you could just leave it to decompose for a little extra fertilizer, this is not a good idea. That’s because there might well be diseased leaves or pests that you can’t see (and their eggs) which might be waiting on the dead plant and could transfer to your healthy ones. So, remove the dead plant and keep it out of your compost pile for good measure.