I guess lifespan affects more the top than the other part, hence somewhat dismishing the global risk.
per 1MW, you'll typically have turbine + tower: EUR 1M foundations : EUR 0.5M cable : EUR 0.5-1M other: 0.5-1.5M (electrical equipement, onshore cable, development, finance) In the long run, we're all dead. John Maynard Keynes
So the sexy "engineering" operational risk (turbine+blade stress) is limited to about 20-30% even if it falls down to replacing the whole top, with a premature replacement if needed probably bringing better efficiency and increase in life span.
The rest of the technology has been in place for a while for offshore oil and regular eletrical stuff so I think not really in the "risky" category.
