I spent a number of years as the technical director for one of the multilab environmental testing companies, and through the '90's we had corporate staff that were certain by the early part of the next decade (7 - 8 years ago at this point) all the organic instrumentation would be replaced by immunoassay techniques.
We are driven by regulatory requirements, and until the existing methods (524.2, 525, 624, 625, 8260, 8270) require lower limits, then the bench-top quads will have have a purpose in the typical environmental testing laboratory. We are currently utilizing predominately Agilent (HP) 5971's 5972's 5973's and two Thermo DSQ-II's and these systems are not likely to be replaced since they are more than capable of achieving the levels of sensitivity that are regulatorily required.
Now, we have potentially on the horizon emerging markets which may require us (as an industry) to bring online HPLC-MS (likely triple quad configurations) techniques and GC-TOF, or high res MS, or MS triple quad.
These techniques won't likely replace existing systems (if for no other reason cost) but will be needed for facilities servicing these emerging fields of analytical testing.