Q:

Is there a way to estimate (predict) the half life of a quantitative trading system?

Usually even good performing quant trading strategies work for a while and then return start to shrink. I see two reasons for that which would probably give rise to different analysis:

The Strategy got known by too many traders and has been arbitraged away.
Market conditions have changed (will or will not revert).

A:

I go out on a limb and say No. 
You can of course observe how it does, but making a prediction about how and when it decays is difficult to impossible with any degree of precision.  You'd need a meta-model of the market as a whole.  And, well, if you had that, wouldn't you use that knowledge to make your model better?
That said, you can of course measure pnl and other return characteristics and extrapolate, but that isn't a proper predictive model in my book.

