Perhaps in regard to this question we might distinguish between “noheg (customs of) avelut” and “nichum aveilim.”
The halachot of Shiva are: Mourners do not: engage in work or business (unless truly irreparable loss will result, in which case there is flexibility on this after 3 days) Do not: bathe/ wash clothing or wear clean clothing/use cosmetics/have sexual relations/wear leather/sit on normal chairs (only low stools)/ do not study Torah/ go out except on Shabbat to shul/ do not participate in any entertainment/
Many mourners, however, do not associate shiva only with prohibitions, even if those prohibitions have the purpose of restricting a mourner from engaging in activities that would distract from the real need to grieve.
They understand that "sitting shiva" means being fed, taken care of, and surrounded by family and friends who come to share stories and offer consolation. Yet these activities are still encouraged even if the official halachic prohibitions are not in effect.
So, does the postponement or termination of official shiva mean that there is no nichum avelim? No. The termination (of the prohibitions) of shiva mean just that, that these prohibitions are lifted. The obligation and opportunity to comfort mourners by visiting them, sitting with them, feeding them, davvenen' with them... all remain operable.
Look at this informative passage in Talmud (Sukkah 41b and elsewhere) which states:
"Kakh haya minhagan shel anshei yerushalayim, adam yotze mi-beito u-lulavo be-yado, holekh le-veit ha-knesset lulavo be-yado, koreh ba-tora ve-nose kapav, maniho al gabbei ha-karka, holekh levaker holim u-lenachem aveilim lulavo be-yado"
It was the custom of the people of Jerusalem that when a person left his home, he would take his lulav, he would go to the synagogue with his lulav in his hand, when he would read the Torah or pronounce the priestly blessing, he would place the lulav upon the ground, he would go to visit the sick and to comfort mourners with his lulav….
So obviously there was comforting of mourners even on Chag. "Mai evel ika ba-hag?" asks Sharira Gaon. "Af al pi she-ein noheg avelut bi-mei he-hag, ela she-chaverav holkhin etzlo, ve-yoshvin etzlo, kedei leyashev da'ato, ve-ka midamei la tana leha milta ke-mi she-ba lenahem avelim."
In other words, while technically there is no formal aveilut on Chol Ha-moed, the bereaved still grieve, and friends visit to alleviate their suffering.
So yes, even when there is no official “shiva,” be with them and the family, share a meal of consolation, ask them to take out photographs and share stories... offer friendship, comfort, caring.... and help them be surrounded by the people who support them.