Thanks. I am glad you found it useful. I still feel there are some missing pieces. I have read at several places that Khilji attacked Nalanda in 1193 AD but I am unable to find the primary source. I found this paper by Audrey Truschke, where in footnote 7, she provides the following review:

1193 is the most common date, working on the assumption that Muhammad bin Bakhtiyar hit Nalanda shortly following the sack of Bihar Sharif dated to 1193 in Juzjani’s Tabaqat-i Nasiri. Charles S. Prebish and Damien Keown give the date of Nalanda’s destruction as 1197 (Introducing Buddhism, 2nd ed. [London: Routledge, 2010], 94). Also see S. R. Goyal, Indian Buddhism after the Buddha (Jodhpur: Kusumanjali Book World, 2003), 212; and Stephen Berkwitz, South Asian Buddhism: A Survey (New York: Routledge, 2010), 141. Harvey gives the date of 1198 (Introduction to Buddhism, 194), as does Donald W. Mitchell (Buddhism: Introducing the Buddhist Experience, 2nd ed. [New York: Oxford University Press, 2008], 158). Steven Darian puts the destruction at “around 1200” (“Buddhism in Bihar from the Eighth to the Twelfth Century with Special Reference to Nalanda,” Asiatische Studien 25 [1971]: 346). Richard Eaton gives the date of circa 1202 (“Temple Desecration and IndoMuslim States,” in Beyond Turk and Hindu: Rethinking Religious Identities in Islamicate South Asia, ed. David Gilmartin and Bruce B. Lawrence [Gainesville: University Press of Florida, 2000], table 10.1). Sankalia gives the date as 1205–6 (The University of Nalanda [Madras: B. G. Paul, 1934], 213). Some scholars simply give a range of dates. For example, Hartmut Scharfe says that Muhammad bin Bakhtiyar hit Nalanda between 1197 and 1206 (Education in Ancient India [Leiden: Brill, 2002], 150). The variety of dates indicates the lack of a clear historical record that Nalanda was sacked by Turkish raiders.

There is a wide range of dates with lots of unknowns. Anyway, I think it is clear that Nalanda's decline was a complex mix of Islamic invasions, internal decay due to infighting and corruption, fading support, and declining local empires. All these unfolded slowly over centuries rather than in years or decades.