Francis V, Duke of Modena, refused consent to the marriage of his niece (Archduchess Maria Theresa of Austria-Este), unless her potential husband renounce his succession rights to the said throne. I assume that the rest of the line of Prince Luitpold likewise rejected the Greek inheritance.
The current Wikipedia article actually states that today's heir is Prince Leopold -- a descendant of King Ludwig I through his youngest son, Prince Adalbert. But as I understand it, this Bavarian prince (a good friend of the Swedish king) is a Roman Catholic. So how could he be the distant heir to King Otto of the Hellenes?