There is no doubt that the condition you describe can occur and does occur. The Vertrees reference "Japanese Maples", all editions, describes a number of fungal infections, Fusarium being one that can attack branch tips and buds as well as the bark tissue at or near ground level. This type of external infection is typically a disease of seedlings or young grafts, and more so in the greenhouse setting. Buy, we can see this sort of dieback on branch tips, especially new growth, if we force it too late in the season and we leave soft nitrogen-rich growth to overwinter. This soft growth can also be attacked in summer if we have a situation with poor drainage and excess nitrogen, one that I have had to deal with and have described before. In this type of stituation, a correction of cultural contions is a must. Any blacked or dead wood should always be pruned at first opportunity to prevent spread. Sometimes removing a blackened young twig just above the next health bud pair can stop the infection that might have continued to travel down the twig. The pruning in combination with recognizing and correcting cultural conditions can clear up the problem for us without chemical treatment which is often uneffective. Many of us are buying smaller and smaller maples now in an effort to acquire new and more rare varieties. Young maples are very suseptible to various fungal and bacterial blights and we as end-growers of these very small plants are being faced with issues that only the primary growers used to be concerned with on a regular basis. While a 5gal or larger plant can easily recover from some twig dieback or a minor fungal attack, a young 1 or 2 year plant faces death when faced with the same attack. While I cannot be certain, here in my neck of the woods, I face a much greater challenge with systemic pathogens than I do with external fungal infections. I do get some mildew in the summer, but I have not lost a plant to that, to my knowledge. Some common treatments I use or have used are Lime-sulfer and dormant oil. I have used Phyton 27 (soluable copper sulfate) both alone and in combination with a Bayer disease control product containing the antifungal tebuconazole. I have mixed the tebuconazole with the Phyton in the same sprayer on occassion. Copper sulfate is advocated by some as a soil drench near bud break to help erradicate some soilborne pathogens. All except the sulfer and oil can be applied during the growing season, but I have applied sulfer to some supposed pseudomonal lesions on the lower trunk area of a maple or two with success. I would consider these applications accessable to the home gardener--there are many many more products. I can hear the backlash against blind application of chemicals, so I must say that it is best to have some idea of what you are treating and just treat the infected plants. I don't always work that way, but I am not that refined yet. While there is a good deal of preventative spraying that goes on with many sorts of plants, we should not have to do that for maples. A healthy plant in good culture should not need preventative spraying of any type and I cannot advocate that. For containerized plants may benefit from the spring soil drench as a bit of insurance. Anyway, we can handle the rest of this discussion on a case by case basis as I have gone on long enough.