The current landmasses of the Earth, continent and archipelago alike, have changed dramatically throughout history. The coastlines of these varying landmasses are, in one sense, the result of the frozen to the non-frozen ratio of water on the planet. In other words, the amount of water on Earth that exists as ice, is not increasing the water levels worldwide and altering the current coastlines we see significantly.
Of course, this will not necessarily always be the case, and in fact, the amount of ice on the planet and worldwide water levels are changing. Human intervention and release of carbon into the atmosphere is a major contributor to loss of ice masses and thereby leads to more of the water on Earth unfrozen and in the general water supply, causing the oceans and other bodies of water worldwide levels to rise and potentially threaten large coastal regions and forever alter coastlines and swallow entire island chains whole.
According to the estimates of what a complete loss of all ice mass into the ocean would do, entire regions of each country would be partially or completely submerged and likely completely destroyed throughout most of these areas. The Coastal regions of North America, for example, would see the loss of nearly the entire state of Florida and much of the Atlantic Northeast as well as a huge loss of area in California. Elsewhere the story would be similar, from Buenos Aires in South America to Stockholm Sweden world renowned cities would be underwater, likely irrecoverable and if nothing else certainly uninhabitable.
Finally, a word of warning related to the scenario laid out thus far. This possible future may not be as remote of a possibility or even as far in the future as you think. An Antarctic ice shelf, the Larsen C, is in the process of breaking away from its primary mass and will soon be the largest icebergs on Earth. This is not a hypothetical scenario. This ice shelf, at 175 km long, is already on its way toward the Ocean, the fate of the rest of our planet’s ice mass is yet to be determined.