Is anything incumbent upon me after I entered into the state of Ihram for Hajj, then was unable to go to Makkah due to the unavailability of transportation because of heavy rain, which forced me to return home and exit the state of Ihram?

As long as you have entered into the state of ihram (definition) for Hajj, it is not permissible to exit ihram due to fear of missing Hajj. Rather, what was obligatory was to take the necessary steps to reach Arafat for the standing before the dawn of the Day of Sacrifice. You remain in your state of ihram, and what is now obligatory upon you, after missing Hajj, is to exit ihram by performing an Umrah (definition), and to offer a sacrifice. If you are unable, then you must fast for ten days, and you must perform Hajj as a make-up in the coming year. Many scholars are of the view that what you did of the prohibitions of ihram during your ignorance of the ruling incurs nothing upon you, but some of them hold the view that a fidyah (definition) (expiation) is obligatory for them.