This is a trend that happens a lot with bounty campaigns this days for blockchain projects, the truth is if a project doesn't meet its hardcap it is almost impossible to pay out the entirety of the bounty budget.
I think a change of approach should be adopted, projects should have a bounty budget that they will be capable of paying as long as the soft cap is reached.
This may mean a smaller budget but it also ensures hunters don't just join out of greed and spam repeatedly.
At the end everyone is happy
Your suggested approach is a workable one that needs to be considered really because the case of bounty hunters not getting paid as a result of the target not being is really alarming but again it won't solve the problem rather it would abate it a little because it would be like giving a free card to project that could not make the soft cap to just go free without paying. The lasting solution I see is the rejevenation of the crypto world where the trust would be returned but only given to those project that have proven themselves to be potent and everyone would be happy.