I am not certain how banks are operating at the moment, given the crisis.

Your HELOC lender does have the option to close your HELOC when you pay them off, but from my experience, that usually doesn't happen unless there is some type of financial crisis. 

I just heard mitt Romney say something regarding the foreclosure crisis that we shouldn't be holding back foreclosures but let the process continue and let the market bottom out and let INVESTORS purchase properties and prices will rise.

Are there any other entities or individuals to which you attribute responsibility for this economic crisis?  

Prior to the financial crisis, you could get 100% financing. 

However, I have a nagging fear that the USA may suffer a major financial collapse, currency crisis, major war, or other catastrophe that could prove to be a challenging environment for anyone who is highly leveraged to survive financially.

In my area (yours too i'm sure) rental demand has been hot since 2007-2008, mainly due to the financial crisis but also due to what i see as an urban revival- more affluent people moving into urban areas than before.

The lack of any mention of it during this financial crisis makes we wonder about the courage of its supporters.

They were sold to various companies to be packaged into mortgage backed securities, which were in turn carved up into other securities.Some of the loans have been carved and sold multiple times and because of the poor record keeping leading up to the financial crisis, often it's hard to prove who owns the loan.Good luck.

Couple things I would note:- Brooklyn (and Manhattan) real estate is at pre crisis highs.- Rent / value ratios on normal rentals are about the worst in the country (except maybe SF).- As mentioned, AirBnB is an ongoing battle in NY.