If your outcome is defined on a continuum, then the expectation value is the sum of product of (probability of some event times the outcome value of that event).
Fair coin flips have 50/50 odds. If we say that you get $100 if it comes up heads, and $0 if it comes up tails, then the expectation value for the money you'd have afterwards is $50=0.5*$100 + 0.5*$0.
If it was an unfair coin with 30% odds of coming up heads, then your expectation value is $30= 0.3*$100 + 0.7*$0. And so on. The fact that the outcomes are dollars or damage percentages is irrelevant to the calculation.
Fair coin flips have 50/50 odds. If we say that you get $100 if it comes up heads, and $0 if it comes up tails, then the expectation value for the money you'd have afterwards is $50=0.5*$100 + 0.5*$0. If it was an unfair coin with 30% odds of coming up heads, then your expectation value is $30= 0.3*$100 + 0.7*$0. And so on. The fact that the outcomes are dollars or damage percentages is irrelevant to the calculation.