Must a vow be fulfilled if what was vowed is lost after it has been obtained?

Whoever makes a vow contingent on the occurrence of an event must fulfill it immediately upon the condition being met, whether the event continues to exist or ceases to exist. This is based on Allah's saying: "They fulfill [their] vows and fear a Day whose evil will be widespread" (Quran 76:7), and the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him."