What happens to a bride whose groom goes insane or disappears after kiddushin but before nissuin? Is she considered agunah or permitted to remarry?
Kiddushin make this woman prohibited to all men except her husband, despite that there is no nisuyim. She cannot remarry if he is yet alive and did not give her a Get. Source: Mishna Kiddushin.
She is bought with money.
Yikar Tosfot Yom Tov (in name of the Ran):
לְבַעְלָהּ לְהַצְרִיכָהּ מִמֶּנּוּ גֵט. הָרַ"ן:
She needs a Get.