they probably won't be deleted, very often bounties are divided by week meaning that for example you can participate during the first week and then stop to participate but you will still receive your stakes for the first week, your stakes will not be deleted, you will receive the stakes for one week times the number of week you completed the bounty tasks
Yeah, that's exactly what happens. They ask you to report your posting and work on weekly basis and if you report that then you are in for that week irrespective of whether you continue to stay with them or not. You'll get your reward if you've really done that work because they do verify it.