In testing my tester for the 4Mx8 10ns 5V SRAM module a couple of weeks ago (data sheet available here), I found, by accident, that the bus capacitance held the data reliably for over a millisecond (a million nanoseconds) in the absense of anything driving the bus. This was of course with all CMOS, ie, no 74LS or other non-CMOS loads on the bus. I did not experiment to find out how much longer it could go, like a whole second or what. Anyway, it definitely was not collapsing after a few dozen nanoseconds, or even microseconds.