If ASICs are ubiquitous, you can expect the ASIC energy output to come close to that of GPUs, there will just have to be a lot more of them mining.
Today a typical rig costs a thousand dollars for the hardware and consumes $75 / month of electricity.
Amortize that 18 months, and you have roughly 40% of the monthly costs going to the hardware and 60% going to electricity.
A thousand dollars worth of ASIC (e.g., a 1/15th of an BFL SC mini rig) consumes about $10 / month of electricity.
Amortize that the same 18 months and you have roughly 85% of the monthly costs going to the hardware and 15% going to electricity.
ASIC mining is 7.5X more efficient then (consumption of $10 / month of electricity versus $75 / month) when including the amortized cost of the hardware.
The unknown is how long to amortize. if it is longer than 18 months then electricity as a % rises. If it is shorter (e.g., faster ASIC comes out) then the cost of electricity as a % of expenses drops.
So I don't think today's miners will be consuming anywhere near as much electricity (e.g., 7.5X less in the example I just gave) with ASIC presuming they aren't going to increase their investment over what they were spending for GPUs.