Vishnu Puran I.3.8-12
"Oh, best of sages! Fifteen twinklings of the eye make a Kastha; thirty Kasthas, one Kala; and thirty Kalas, one Muhurta. Thirty Muhurtas constitute a day and night of mortals: thirty such days make a month, divided into two half-months: six months form an Ayana (the period of the sun's progress north or south of the ecliptic): and two Ayanas compose a year. The southern Ayana is a night and the northern a day of the Gods. Twelve thousand divine years, each composed of (three hundred and sixty) such days, constitute the period of the four Yugas (ages). They are thus distributed: the Krta (Satya) age has four thousand divine years; the Treta three thousand; the Dvapara two thousand; and the Kali age one thousand: so those acquainted with antiquity have declared."
At the end of each Caturyuga, Vedas perish, and Saptarishis come down on earth to restore the Vedas. Manvantara (One Manu's period) comprises 71 such Caturyugas. At the end of 14 such Manus, one Kalpa (one day of Brahma) is over. The deluge takes place (one night of Brahma), and the universe perishes. It is consumed with fire. After completing 360 such Ahoratras (one day and one night of Brahma), Brahma completes 1 year (Brahma Varsha). The life span of one Brahma (Mahakalpa) is 120 Brahma Varsha. So at the end of this period, Brahma himself perishes. After the death of Brahma, a great flood (Mahapralaya) comes. (from Vishnu Purana I.3 and Manavantara discussion in Puranic Encyclopaedia by Vettam Mani)
The Caturyuga scheme is described in the Puranas. Here I quoted from Vishnu Purana. There could be a slight variation between different Puranas. But overall, this is the scheme.
You can clearly see that scripture talks about a really long period (in human years), not 5000 years!
Your second question, I think, is opinion-based.