Here is a book chapter on this topic:
Mazza, C., Riccaboni, A., & Quattrone, P. (2008). Found in translation: On the persistence of the university as institution. European universities in transition: Issues, models and cases. Northampton: Edward Elgar Publishing.
These authors argue that the longevity of traditional universities is due to their socially legitimated role to "make ideas, people, and disciplines meet and cross-fertilize". For centuries, this role was manifested in such artifacts as great libraries (and later university presses) and degrees for the elites in government, religion, and (to a lesser extent) business. Of course, being self-sustaining financially (endowments) and physically (buildings and infrastructure) has been an important factor.
Historically, the university was the first institution in human history to systematically question itself as part of it's very constitution. From the start, the communities of scholars engaged in systematic inquiry and critical debate on the subjects of study, and even the way those subjects were investigated and taught.
Though far from perfect, this self-critical capability gave universities the capacity to take in and develop new knowledge and to let go of knowledge systems that no longer had intellectual support. For most of their histories, universities shaped the educational norms of the society around them -- at the national and international elite levels, at least -- rather than being shaped by those elites. The certainly weren't responding to the changing educational preferences or needs of the general public. Other institutions filled in this role (gap), including public universities, land-grant colleges, community colleges, polytechnic institutes, and so on.
The oldest universities in continuous operation are:
- University of Bologna - 1088
- Oxford University - 1167
- Cambridge University - 1209
- University of Salamanca (Spain) - 1218
- University of Padua - 1220
- University of Naples Federico II - 1224 (first public