R. Chaim Brisker (Chiddushei HaGrach al haShas, p. 1) maintains that there is a fundamental difference between the insertion of Ten Tal U’Matar L’Vrakhah into the amidah and that of Ya’aleh V’Yavo. Ya’aleh V’Yavo is an obligatory reference inserted into the amidah; it is possible that its omission does not invalidate the entire prayer (even though the prayer must nonetheless be repeated to facilitate its recitation. Ten Tal U’Matar, however, becomes part of the format of the amidah itself, and thus its omission is as if the entire prayer was not recited.

R. Tzvi Pesach Frank (Resp. Har Tzvi, I, 54) argues that the opposite is true, and if anything, Ya’aleh V’Yavo is more a part of the structure of amidah than Ten Tal U’Matar is. As proof, he notes that Ya’aleh V’Yavo is recited only as part of “r’tzeh”, and if one forgets and starts “modim”, he must go back to r’tzeh (Shulchan Arukh O.C. 422). Ten Tal U’Matar, by contrast, is more flexible; and in the event of an omission caught before “shomea tefilah” the insertion can be made at that point. (O.C. 117:5).

He then notes the opinion of the Chesed L’Avraham (Tinyana, 20) that concurs with his, and rules as well that if one omits Ten Tal U’Matar at ma’ariv he does not repeat the prayer (although the implication of the Magen Avraham, 236:1, is otherwise). This is due to the fact that ma’ariv is a reshut, and even though in practice, it has been accepted as obligatory, that is only in reference to the prayer itself. Ten Tal U’Matar, as an additional reference, does not benefit from any absolute commitment to recital at ma’ariv. Since its omission does not invalidate the prayer, there is no need to repeat ma’ariv.

Tosafot (Berakhot 29b, s.v. ta’ah) rules, in the name of the Behag, that one who omits an additional reference, and is required to repeat the amidah, can instead listen carefully to chazarat hashatz and that would suffice. The Chavatzelet HaSharon al HaTorah (Bereishit, p. 433) suggests that this derives from the fact the amidah has two functions: invoking divine mercy, and worship, patterned after the sacrificial order. It is improper for one who knows how to pray to rely on chazarat hashatz, because of the requirement of the Yerushalmi (Berakhot 3:3), that “every individual should request mercy on himself”. However, one who has prayed, but omitted an additional reference, has already “request mercy on himself”. The need to include the reference is a function of worship, every day as is appropriate for that day. Thus, this element can be fulfilled through chazarat hashatz, and thus the Behag’s position (see also Resp. Minchat Yitzchak, X, 40).