With rising tuition, the need to attain specialized knowledge earlier and earlier, and the massive funding cuts to state institutions, college has become more precarious, isolated and marginal. While undergraduate students will exceed a record 20 million within five years, only a small fraction will experience college in the traditional sense. Most will either attend online or vocational programs, and, at most, only 40 percent will get a degree — and, on average, a college graduate will incur more than $25,000 in student debt. In his new book, “College: What It Was, Is, and Should Be,” Columbia professor Andrew Delbanco acknowledges that the hour is late, but there’s still time to save this valuable institution. Can college be saved?