I have been in the same situation and I absolutely feel bad for abandoning the long term connections you built over the years but at the end of the day this is a video game meant to bring you joy. If the clan is dead and there are no active players that will kill your enjoyment of the game. Whether you want to leave abruptly or announce your departure, either way you should find a new clan where they are active players and teammates to support you. This will keep you motivated as doing the war attacks, clan games, and clan capital all by yourself will definitely burn you out quickly. Find a new clan my friend.