On my end, long running bounties paid via their own coin or token have high chance that you will not get anything out of it because the possible scenario of abandoning the project is high.
Based on my experience yes, I have participated a bounty in the past and they extend the bounty because they can't collect the right amount they needed.
Also, there's no guarantee that they will be able to collect more if they will extend because usually good projects can easily get sold out, some even in minutes they are sold out already.
If they see that their project is not gaining support from the community or they have no enough funds to continue, they will just disappear without informing those bounty hunters that are promoting them.
That's gonna be a waste of time then.. for me, I would just look at a bounty that will run in 1 month, so if it will extend for another month, it will not hurt us a lot since 2 months are not that long provided the task is easy.