That totally sucks.
Here's what happened in '01.
I recall one consulting firm upfront just stated "sorry, we're going to have to renege on your offer." No it wasn't McKinsey, Bain or BCG.
Many others though played this "deferral" game - by deferring your job offer by 6, 12, and sometimes 18 months. It's a way of reneging on your offer without actually having to officially "renege" on your offer.
Also, there's no guarantee that you will have a job by the end of that deferral.
Remember that when you get the job offer, it's an OFFER. There is no guarantee of employment whatsoever.
And a verbal guarantee from a consultant is about as good as one from a used car salesman.
They're basically weaseling out of being direct, by playing language games.
What happened is that after the "6 month deferral", they would then defer it yet again. And again. Until you get the hint.
It's sort of like dating - the person rather than say, "I'm sorry, this won't work out" will simply say "you know, I'm really busy, call me back in a week or so". And then you call back and the person says "oh, yeah, well I'm sorta busy now, call back later or better yet, I'll call YOU back, 'kay? Buh bye." That person ain't calling back.
I am no fans of the personalities/culture in investment banking, but at least they're pretty direct about things. If they are going to fire your ass, they will tell you. If they are going to renege on your offer (which quite a number of them did in '01), they will tell you upfront rather than play games with "can we defer your offer by say, oh, how about...7 months? Sound good? Aw, you cheeky monkey, go have yerself a good 7 months there, tiger!"). Management consultants are like snake oil salesman. Do NOT be sheep and fall for their words hook, line and sinker. Treat everything they say with a HUGE dose of skepticism. When consultants get in trouble, they will HIDE, DODGE, and SPIN.
Management consultants are far better at spin and misdirection than they are at telling the truth directly. Ignore this at your peril.
Remember that they do corporate propaganda better than anyone else. And that includes the recruiting razzle dazzle shows they put on for you on campus, ready to make you feel real special and to really make you feel like you will be *truly* working on Important work with a capital "I". That they are truly peachy.
Drink the Kool Aid wholeheartedly, and you will find yourself screwed. Spin, spin, spin, spin, and more spin - that's what they do for a living -- and they will do it to you, even with your job offer.
Anyhow, even mighty McKinsey suffered in '01. The firm instituted a capital call back then (an open secret within the consulting community) - meaning that the company was short on cash, and had to literally ask the partners to pony up cash to fund the firm temporarily. Ah, the joys of partnership.
Should you get a "deferral" from a consulting firm, no matter WHAT they say, treat it as a reneged offer. Put your full effort into finding another job without the expectation of ever hearing from these consulting firms again.
I repeat, do NOT hold out hope that they are good on their word for their deferral. It's a reneged offer.
Don't do a CNBC and trust everything that comes out of the mouth of someone who speaks corporate. Doesn't mean they're always lying, but for your own sake take everything they say with a healthy dose of skepticism.