That was another option considered yes, but it was rejected by most of the US high command. The Navy and King in particular were less supportive and did prefer to simply continue to blockade and bombard the islands from everything from B-29's to carrier strikes, to simply taking surface combatants and cruising the cost to shell targets.

There are some problems with that plan though. The first is that Japan could not get any more isolated really. By Spring of 1945 virtually the entire Japanese merchant marine was either sunk or unable to leave port for lack of fuel, ith the IJN no better. Which meant that oil, natural resources, and even foodstuffs were unable to be brought to the home islands from the "Southern Resource Area" and hadnt been for most of 1945, in addition to an effective mining operation in the Sea of Japan itself by aircraft and USN subs meant any travel by water was already a no go. This on top of the continuous bombings meant that after 6 months you really had reduced much of Japan's infrastructure to rubble, there just wasnt that much left to destroy.

But as seen by events those efforts brought no willingness in the Japanese government to come to terms, so a continuation fo that policy would have had to be very extreme and harsh, literally designed to salt the earth of the home islands.

It would have become essentially the intentional starvation of the Home Islands, starting with the civilian population, which shortages and lack of supplies had already begun to hit. It would have taken months or longer, with many other deaths first before the military would have seriously been compromised enough, and even then it is no guarantee that you get terms.

You also have national morale at home to consider. Saying you plan is to starve the entire nation to death doesnt look that great, even compared to the normal waging of war, especially as much of you war effort is based upon that being the sort of thing your enemies do and you are fighting to protect the world from such barbarism.

And then finally much of US high command was conscious of how much time that would take. Original estimates in 1943 thought that it would be 1947 for an invasion could take place but by 1945 they found themselves ready, and having seen the nation eager for the war to be over after the surrender of Germany they worried any prolonging of the war would build pressure at home to drop the unconditional surrender and negotiate, because of the lack of obvious progress and the continued loss of US servicemen through enemy action, disease, or just plain accidents.

You also then of course did have the Russians who had their own plan and agenda. An invasion of the Home Islands was most likely beyond their small navy to support, but as it happened they could have gobbled up more of the Japanese occupied mainland then they did, which would have been unpopular for the US, in particular it would have further weakened the US friendly Nationalist Chinese.

So int he end the potential deaths from an invasion were found preferable to US decision makers over waiting for something that might never come, and basically hoping enough of them starved before the next election which could have forced a change in the demand for unconditional surrender.

However if an invasion HAD become necessary it does raise an interesting question. The CNO (top naval officer) Ernest King was very against it by the time August 1945 comes with Nimitz(Commander of the Pacific Fleet) supporting him. So if it had come time to draw up final plans and begin drafting the orders it is possible that Truman would have been faced with a divided High Command, and would have had to pick in essence which service to support, and it also would have tested how committed the top Army General, Marshall, was to supporting MacArthur who was the driving force behind the plans, in particular in light of intelligence which suggested the Japanese were concentrating forces against US landing areas in the South and around Tokyo.

It is interesting to note that the US Strategic Bombing Survey in 1946 concluded that Japan probably would have been forced to surrender soon anyway because of their isolation and lack of resources.

Based on a detailed investigation of all the facts, and supported by the testimony of the surviving Japanese leaders involved, it is the Survey's opinion that certainly prior to 31 December 1945, and in all probability prior to 1 November 1945, Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war, and even if no invasion had been planned or contemplated.

It is worth taking the USSBS with a grain of salt, because it was written by people who felt that the atomic bombs threatened their legacy (by taking all the credit) and future livelihood (by making people think that a small conventional military might be enough) but the idea is not a far-fetched one in any case.