Again, the point isn't that Truk was doomed. It's that the soldiers did not surrender until instructed to, by the emperor, despite their doom being obvious to anyone with a pulse. Truk could be bypassed, so it mattered little whether or not the garrison surrendered. The home islands couldn't.
Which raises the question - if blockading and cutting Truk worked for Truk - would it not work for the Home Islands?
Japan does not have the natural resources to sustain herself. Japan relied, then as now, on importation. The folks in the garrison were Japanese soldiers. Do you think that the people of Japan would have been able to hold it together in a blockade? I don’t see it.
The options were not ‘invasion’ or ‘atomic weapons’. There was a third option, blockade.