You're right. To expand: don't bother is the null. Deciding to cover-up leads to one of two outcomes, the good one (you get away) and the bad (you get boned). You don't know which of those outcomes you'll get.
The percentages the comment you're responding to provides aren't probabilities, but damage fractions; 50% isn't a 50/50 likelihood, but 50% damage of the 100% case.
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.
The percentages the comment you're responding to provides aren't probabilities, but damage fractions; 50% isn't a 50/50 likelihood, but 50% damage of the 100% case.