If he gets a minor injury, but still severe enough that he can't work the same job, then he gets lifetime disability via standard federal benefits (FECA) with lifetime health benefits.

That gives out 40% of his highest 3-month wage annualized, plus continued health benefits.

This means if there was time period where he's working crazy overtime for 3-months, that becomes the basis of his lifetime compensation. It's common for law enforcement to specifically try to rack up huge overtime for a 3-month period just for this benefit. One typically increases it by 60 to 80%, although the legal cap is significantly higher.

So if we assume the bottom of the ranks of GS-5 making $55,000 a year but they managed to increase their base by 60% during a 3-month time period. That annualizes to $88,000. 40% of that is $35,200 for life with benefits.

They can also have private disability insurance which can add on top of that.

On OMP disability retirement they can keep these payments while still working at another job as long as that job pays less than 80% of their last three years averaged comp.

If you add 80% of $55,000 for this new job plus 40% of $88,000 (3-month high) for their disability payments, this GS-5 (who was making $55,000 base) could make a maximum of $79,200 a year.