Dear Rabbi Kornfeld:
(a) Thank you for your answer below--but I would think that on the first day that the grogros are put on the roof-it is still edible?
(b) Also, could you tell me why on daf 55a -- there was a "tov" put on the forehead of both the Reshayim and the Tzadikim--why not just one and the others would be saved or killed by default?
(c) I once asked you why all the names of the Sedorim are plural except for Moed--I didn't seem to have gotten the answer and I am afraid I might have missed it.
(d) I once saw in Rambam's hilchos isurei beeyah that during the times of Shlomoh Hamelech (and also Dovid haMelech) the Beis din did not accept geirim...if a beis din of hedyotos made geirim then they stayed Jewish even if they went back to Avodah Zorah....but how could Shlomoh Hamelech (the Yedid Hash-m) accepted geirim of a beis din of hedyotos as his wife(s)?
(a) From RASHI (DH Ela, and in Beitzah 26b, DH Heichi Dami) it seems that they become inedible immediately .
(b) The "Tav" represents Midas ha'Din, Hash-m's attribute of strict justice, and it also represents Midas ha'Rachamim, His attribute of mercy. On the foreheads of the Tzadikim, it symbolizes that they are beneficiaries of Hash-m's mercy and are protected even when they are not totally righteous ("Tzadikim Gemurim") and they are fit to be saved at a time of plague, even when they live among Resha'im. On the foreheads of the Resha'im, it symbolizes that they are subject to Midas ha'Din, showing that they are to die even if they have some merits, and even if they do not live among other Resha'im and the plague would not have reached them otherwise.
(c) Rav Moshe Shapiro, shlita, and Rav Hillel Ruvel, shlita, both told me that the name of Seder "Moed" is in the singular form because all of the festivals compose a single, continuous structure throughout the yearly cycle. They are not separate entities; rather, they are interconnected with each other in such a way that they form a complete and unified system. This is discussed in detail by the MAHARAL (Gevuros Hash-m, ch. 35). (An English book will be published soon on this topic, called "Seasons of Life" by Noson Slifkin.)
(d) Your question is based on the Gemara in Yevamos (24b) and the RAMBAM in Hilchos Isurei Bi'ah 13:15. It seems that Shlomo ha'Melech saw a need to convert them, either for the sake of the peace of the kingdom (in cases where he married the daughters of kings of other nations), or in order to bring closer the Ge'ulah, by way of bringing to fruition the sparks of holiness that lie dormant among all the nations (as the Ba'alei Machshavah describe).
The Rebbi (shlita) of the Daf I go to tried to find the "MAHARAL (Gevuros Hashem, ch. 35)" that you mentioned and told me that he didn't find anything there--perhaps it is in a different chapter?
Also, why does the torah call the Moadim ie Moadei HaShem, Moadeichem and even the word from which the name of Moed is learned from--Itecho -- are all plural?
(a) I'm sorry -- I mis-referenced it. It is Gevuros Hashem, chapter 46.
(b) The Torah certainly must use the plural form, because each Mo'ed must be observed in its own right. However, the root of all the Mo'adim are all based on a single foundation, as we mentioned.
When the Torah writes "Itecha," it is referring to the festivals which one must observe in a practical, and is not referring to the deeper foundation of the festivals. (See what we wrote in Insights to Berachos 52b, regarding the foundation of fire as contrasted to the actual, physical fire. That differentiation is similar to the one between the practical observance of the festivals and the underlying foundation of the festivals.)