It only took seven months for investment banking as we know it to collapse. Between March and October, each of the five major U.S. independent investment banks either disappeared or changed their stripes entirely. Firms with pedigrees as venerable as Bear Stearns Cos., Lehman Brothers Holdings Inc. and Merrill Lynch & Co. -- institutions that had survived the Great Depression -- were lost to acquisition or bankruptcy. Goldman, Sachs & Co. and Morgan Stanley, meanwhile, ran into the protective arms of the Federal Reserve and converted into bank holding companies, trading their lightly regulated independence for access to the Fed's lending apparatus.

"We are entering a whole new world that no one has seen before," says Gerard Cassidy, analyst at RBC Capital Markets. "The traditional monoline investment banking model is gone."

True enough. But what does that mean for the institutional banking business? Perhaps not much.

An era on Wall Street has surely ended. Gone are the exaggerated expectations that helped fuel the business' outsized appetite for risk and return. But the need for the underwriting and advisory services that investment banks provide isn't going away, even if it's in hibernation right now. Indeed, the five monolines still exist to service that need; they just exist in a different form.

Take Lehman Brothers, for example. The name might be gone after its bankruptcy and acquisition by Barclays plc this fall, but much of the investment bank's infrastructure has remained intact. Its bankers, or at least most of them, are still plying their trade, though within the more restricted ambit of a global commercial bank. The same could be said for Merrill Lynch, which agreed for Bank of America Corp. to buy it on the same day Lehman disintegrated. Even the newly minted commercial banks, Morgan Stanley and Goldman Sachs, won't be radically transformed overnight. In fact, they have as long as five years to comply with commercial banking rules, which might require them to shed some minor subsidiaries.

The monolines' new commercial bank classification becomes even more meaningless when you consider that the big universal banks control the lion's share of the underwriting and advisory business. According to research firm Dealogic, the top three global debt capital markets bookrunners in 2007 were the commercial banks Citigroup Inc., J.P. Morgan Chase & Co. and Deutsche Bank AG, which underwrote a combined 20% share of the year's deals. In equity capital markets, UBS, J.P. Morgan and Citi stood atop the rest, with a combined 22% market share.

That's not to say there hasn't been -- and won't continue to be -- great change imposed upon the investment banking business. Some of it may even be quite dramatic. For one thing, it's clear that banks of all kinds will be much less profitable (once the banks actually return to making money). That will be especially true for Morgan Stanley and Goldman Sachs, which once boosted their profit margins with leverage ratios as high as 30 times but are now rushing to shrink them in line with the 13 times of the J.P. Morgans of the banking universe.

Says RBC's Cassidy, "We are going to see lower leverage, lower profit and lower growth."

There will also undoubtedly be fewer employees, structured products and derivative "technologies," and Cassidy's "whole new world" might not include the large proprietary trading desks or in-house merchant banking arms that helped to goose the giant profits of the past few years. The business will certainly be more tightly controlled, with prognoses of utility-like regulation of banks coming from such pontificators as fund manager and "The Black Swan" author Nassim Nicholas Taleb.

But merchant banks within investment banks, as well as large proprietary trading units, are a fairly recent phenomenon. Both gained force in the late 1980s and early 1990s, just in time for the credit boom that not only pushed investment banking profits to record levels, but also spurred the development of robust private equity, leveraged lending and other balance-sheet-heavy operations within formerly pure-play advisory shops like Goldman Sachs.

"Banks have always swayed with the times," says Halle Benett, Americas co-head of UBS' financial institutions group. "There will be a return to a more traditional model of banking."

That model might feature banks holding more of the securities they underwrite and placing less of an emphasis on risk taking, but that could only serve to create opportunity for others. Indeed, as the existing banks deleverage and retrench, large private equity firms such as Kohlberg Kravis Roberts & Co. and Blackstone Group LP may find the time is right to build their own capital markets arms to disintermediate the firms upon which they were so dependent at the height of the credit craze.

In fact, Kohlberg Kravis Roberts has been making noises of doing that very thing since 2006, when it hired Craig Farr, formerly of Citigroup's equity capital markets, to build a group that would create a syndicate of hedge fund buyers ready to invest in KKR deals, essentially removing the need for the leveraged buyout shop to turn to banks for financing.

In August, KKR even showed some underwriting capability when it joined a syndicate of lenders in a deal to provide $1 billion in debt to finance SunGard Data Systems Inc.'s $400 million purchase of a majority stake in French software company GL Trade SA.

Blackstone acquired debt-focused hedge fund GSO Capital Partners LP last year and was saying -- if not exactly doing -- similar things as KKR. The private equity shop's president, Hamilton "Tony" James, said at the Super Return conference in Munich in February that Blackstone wanted to do an end run around the banks.

"We're bypassing the banks," he said, according to Bloomberg News, in reference to efforts to find financiers in the form of investors who'd buy Blackstone debt. "There's still ultimately demand for this paper out there if you can go directly to the buyers."

There is also opportunity for advisory shops such as Lazard, Greenhill & Co. and Evercore Partners Inc. to grow, says UBS' Benett. "When the large firms are tainted, bringing in other firms is not a bad decision for boards," he says.

Benett cautions, however, that "when capital raising is the name of the game," larger banks have the advantage. "The demise of the large firm is being overstated," he says. "We just have to hit reboot on the last 10 years."

That might oversimplify the challenges banking faces during a severe crisis. But a reboot on the banking model that took hold during the credit boom may not be a bad idea.

As Andrew Senchak, president of financial-services-focused investment bank Keefe, Bruyette & Woods Inc., puts it, "Maybe the period of financial innovation is over. We might have a saner, healthier world."