QWhen playing this follower's On Evolve ability, if I can't select an enemy follower on the field, can I still choose option 2 to discard a non-Runecraft card?

ANo. If you can't select an enemy follower, you would be required to choose option 1. However, you may choose not to pay the cost for either option to have nothing happen.

QIf I have no Runecraft cards in my hand, can I still choose option 1?

AYes. However, as you would be unable to pay the cost, nothing would happen. The same would be true if you had no non-Runecraft cards in hand and chose option 2.