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Possibility of FPGA completely replacing ASIC is almost nil. You can never achieve the timing constraints that is possible in ASIC in an FPGA. Remember ASIC is 'Application Specific', you can tune it for maxx performance timing etc. This is not possible in FPGA since here performance is sacrificed for flexibility and reprogrammability.
But i have heard that FPGA is used in plasma displays and in high end research areas. Anyway FPGA remains best for prototyping.
In high volume (millions of units), FPGAs will usually be a lot more expensive than an ASIC. Also, if you need any analog logic, you'll need an ASIC. Low power designs are another area where ASICs will usually win out.